mirror of
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Made the file pep8 compliant (#2601)
Actually nearly compliant, I ran `pep8 code.py --ignore=E402,E501,E712`
This commit is contained in:
David Haberthür
ven
parent
919e44f843
commit
4737819e5d
@ -5,6 +5,7 @@ contributors:
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- ["Amin Bandali", "http://aminbandali.com"]
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- ["Andre Polykanine", "https://github.com/Oire"]
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- ["evuez", "http://github.com/evuez"]
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- ["habi", "http://github.com/habi"]
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filename: learnpython.py
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---
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@ -34,9 +35,8 @@ Python 3 tutorial.
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as comments
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"""
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####################################################
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## 1. Primitive Datatypes and Operators
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# 1. Primitive Datatypes and Operators
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####################################################
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# You have numbers
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@ -53,41 +53,42 @@ Python 3 tutorial.
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5 / 2 # => 2
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# To fix division we need to learn about floats.
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2.0 # This is a float
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2.0 # This is a float
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11.0 / 4.0 # => 2.75 ahhh...much better
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# Result of integer division truncated down both for positive and negative.
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5 // 3 # => 1
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5.0 // 3.0 # => 1.0 # works on floats too
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5 // 3 # => 1
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5.0 // 3.0 # => 1.0 # works on floats too
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-5 // 3 # => -2
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-5.0 // 3.0 # => -2.0
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-5.0 // 3.0 # => -2.0
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# Note that we can also import division module(Section 6 Modules)
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# to carry out normal division with just one '/'.
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from __future__ import division
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11/4 # => 2.75 ...normal division
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11//4 # => 2 ...floored division
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11 / 4 # => 2.75 ...normal division
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11 // 4 # => 2 ...floored division
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# Modulo operation
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7 % 3 # => 1
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7 % 3 # => 1
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# Exponentiation (x to the yth power)
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2**4 # => 16
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2 ** 4 # => 16
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# Enforce precedence with parentheses
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(1 + 3) * 2 # => 8
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# Boolean Operators
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# Note "and" and "or" are case-sensitive
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True and False #=> False
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False or True #=> True
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True and False # => False
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False or True # => True
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# Note using Bool operators with ints
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0 and 2 #=> 0
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-5 or 0 #=> -5
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0 == False #=> True
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2 == True #=> False
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1 == True #=> True
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0 and 2 # => 0
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-5 or 0 # => -5
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0 == False # => True
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2 == True # => False
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1 == True # => True
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# negate with not
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not True # => False
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@ -129,12 +130,12 @@ not False # => True
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# You can find the length of a string
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len("This is a string") # => 16
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#String formatting with %
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#Even though the % string operator will be deprecated on Python 3.1 and removed
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#later at some time, it may still be good to know how it works.
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# String formatting with %
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# Even though the % string operator will be deprecated on Python 3.1 and removed
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# later at some time, it may still be good to know how it works.
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x = 'apple'
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y = 'lemon'
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z = "The items in the basket are %s and %s" % (x,y)
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z = "The items in the basket are %s and %s" % (x, y)
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# A newer way to format strings is the format method.
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# This method is the preferred way
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@ -170,20 +171,21 @@ bool("") # => False
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####################################################
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## 2. Variables and Collections
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# 2. Variables and Collections
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####################################################
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# Python has a print statement
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print "I'm Python. Nice to meet you!" # => I'm Python. Nice to meet you!
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print "I'm Python. Nice to meet you!" # => I'm Python. Nice to meet you!
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# Simple way to get input data from console
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input_string_var = raw_input("Enter some data: ") # Returns the data as a string
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input_var = input("Enter some data: ") # Evaluates the data as python code
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input_string_var = raw_input(
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"Enter some data: ") # Returns the data as a string
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input_var = input("Enter some data: ") # Evaluates the data as python code
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# Warning: Caution is recommended for input() method usage
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# Note: In python 3, input() is deprecated and raw_input() is renamed to input()
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# No need to declare variables before assigning to them.
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some_var = 5 # Convention is to use lower_case_with_underscores
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some_var = 5 # Convention is to use lower_case_with_underscores
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some_var # => 5
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# Accessing a previously unassigned variable is an exception.
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@ -194,21 +196,20 @@ some_other_var # Raises a name error
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# Equivalent of C's '?:' ternary operator
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"yahoo!" if 3 > 2 else 2 # => "yahoo!"
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# Lists store sequences
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li = []
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# You can start with a prefilled list
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other_li = [4, 5, 6]
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# Add stuff to the end of a list with append
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li.append(1) # li is now [1]
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li.append(2) # li is now [1, 2]
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li.append(4) # li is now [1, 2, 4]
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li.append(3) # li is now [1, 2, 4, 3]
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li.append(1) # li is now [1]
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li.append(2) # li is now [1, 2]
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li.append(4) # li is now [1, 2, 4]
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li.append(3) # li is now [1, 2, 4, 3]
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# Remove from the end with pop
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li.pop() # => 3 and li is now [1, 2, 4]
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li.pop() # => 3 and li is now [1, 2, 4]
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# Let's put it back
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li.append(3) # li is now [1, 2, 4, 3] again.
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li.append(3) # li is now [1, 2, 4, 3] again.
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# Access a list like you would any array
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li[0] # => 1
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@ -230,21 +231,21 @@ li[2:] # => [4, 3]
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# Omit the end
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li[:3] # => [1, 2, 4]
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# Select every second entry
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li[::2] # =>[1, 4]
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li[::2] # =>[1, 4]
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# Reverse a copy of the list
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li[::-1] # => [3, 4, 2, 1]
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li[::-1] # => [3, 4, 2, 1]
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# Use any combination of these to make advanced slices
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# li[start:end:step]
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# Remove arbitrary elements from a list with "del"
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del li[2] # li is now [1, 2, 3]
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del li[2] # li is now [1, 2, 3]
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# You can add lists
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li + other_li # => [1, 2, 3, 4, 5, 6]
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li + other_li # => [1, 2, 3, 4, 5, 6]
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# Note: values for li and for other_li are not modified.
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# Concatenate lists with "extend()"
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li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6]
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li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6]
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# Remove first occurrence of a value
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li.remove(2) # li is now [1, 3, 4, 5, 6]
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@ -258,31 +259,29 @@ li.index(2) # => 1
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li.index(7) # Raises a ValueError as 7 is not in the list
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# Check for existence in a list with "in"
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1 in li # => True
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1 in li # => True
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# Examine the length with "len()"
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len(li) # => 6
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len(li) # => 6
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# Tuples are like lists but are immutable.
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tup = (1, 2, 3)
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tup[0] # => 1
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tup[0] # => 1
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tup[0] = 3 # Raises a TypeError
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# You can do all those list thingies on tuples too
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len(tup) # => 3
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tup + (4, 5, 6) # => (1, 2, 3, 4, 5, 6)
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tup[:2] # => (1, 2)
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2 in tup # => True
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len(tup) # => 3
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tup + (4, 5, 6) # => (1, 2, 3, 4, 5, 6)
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tup[:2] # => (1, 2)
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2 in tup # => True
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# You can unpack tuples (or lists) into variables
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a, b, c = (1, 2, 3) # a is now 1, b is now 2 and c is now 3
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d, e, f = 4, 5, 6 # you can leave out the parentheses
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a, b, c = (1, 2, 3) # a is now 1, b is now 2 and c is now 3
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d, e, f = 4, 5, 6 # you can leave out the parentheses
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# Tuples are created by default if you leave out the parentheses
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g = 4, 5, 6 # => (4, 5, 6)
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g = 4, 5, 6 # => (4, 5, 6)
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# Now look how easy it is to swap two values
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e, d = d, e # d is now 5 and e is now 4
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e, d = d, e # d is now 5 and e is now 4
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# Dictionaries store mappings
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empty_dict = {}
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@ -290,33 +289,33 @@ empty_dict = {}
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filled_dict = {"one": 1, "two": 2, "three": 3}
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# Look up values with []
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filled_dict["one"] # => 1
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filled_dict["one"] # => 1
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# Get all keys as a list with "keys()"
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filled_dict.keys() # => ["three", "two", "one"]
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filled_dict.keys() # => ["three", "two", "one"]
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# Note - Dictionary key ordering is not guaranteed.
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# Your results might not match this exactly.
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# Get all values as a list with "values()"
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filled_dict.values() # => [3, 2, 1]
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filled_dict.values() # => [3, 2, 1]
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# Note - Same as above regarding key ordering.
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# Get all key-value pairs as a list of tuples with "items()"
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filled_dicts.items() # => [("one", 1), ("two", 2), ("three", 3)]
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filled_dicts.items() # => [("one", 1), ("two", 2), ("three", 3)]
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# Check for existence of keys in a dictionary with "in"
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"one" in filled_dict # => True
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1 in filled_dict # => False
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"one" in filled_dict # => True
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1 in filled_dict # => False
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# Looking up a non-existing key is a KeyError
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filled_dict["four"] # KeyError
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filled_dict["four"] # KeyError
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# Use "get()" method to avoid the KeyError
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filled_dict.get("one") # => 1
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filled_dict.get("four") # => None
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filled_dict.get("one") # => 1
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filled_dict.get("four") # => None
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# The get method supports a default argument when the value is missing
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filled_dict.get("one", 4) # => 1
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filled_dict.get("four", 4) # => 4
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filled_dict.get("one", 4) # => 1
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filled_dict.get("four", 4) # => 4
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# note that filled_dict.get("four") is still => None
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# (get doesn't set the value in the dictionary)
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@ -327,47 +326,46 @@ filled_dict["four"] = 4 # now, filled_dict["four"] => 4
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filled_dict.setdefault("five", 5) # filled_dict["five"] is set to 5
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filled_dict.setdefault("five", 6) # filled_dict["five"] is still 5
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# Sets store ... well sets (which are like lists but can contain no duplicates)
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empty_set = set()
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# Initialize a "set()" with a bunch of values
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some_set = set([1, 2, 2, 3, 4]) # some_set is now set([1, 2, 3, 4])
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some_set = set([1, 2, 2, 3, 4]) # some_set is now set([1, 2, 3, 4])
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# order is not guaranteed, even though it may sometimes look sorted
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another_set = set([4, 3, 2, 2, 1]) # another_set is now set([1, 2, 3, 4])
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# Since Python 2.7, {} can be used to declare a set
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filled_set = {1, 2, 2, 3, 4} # => {1, 2, 3, 4}
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filled_set = {1, 2, 2, 3, 4} # => {1, 2, 3, 4}
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# Add more items to a set
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filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5}
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filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5}
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# Do set intersection with &
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other_set = {3, 4, 5, 6}
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filled_set & other_set # => {3, 4, 5}
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filled_set & other_set # => {3, 4, 5}
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# Do set union with |
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filled_set | other_set # => {1, 2, 3, 4, 5, 6}
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filled_set | other_set # => {1, 2, 3, 4, 5, 6}
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# Do set difference with -
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{1, 2, 3, 4} - {2, 3, 5} # => {1, 4}
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{1, 2, 3, 4} - {2, 3, 5} # => {1, 4}
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# Do set symmetric difference with ^
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{1, 2, 3, 4} ^ {2, 3, 5} # => {1, 4, 5}
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# Check if set on the left is a superset of set on the right
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{1, 2} >= {1, 2, 3} # => False
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{1, 2} >= {1, 2, 3} # => False
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# Check if set on the left is a subset of set on the right
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{1, 2} <= {1, 2, 3} # => True
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{1, 2} <= {1, 2, 3} # => True
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# Check for existence in a set with in
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2 in filled_set # => True
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10 in filled_set # => False
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2 in filled_set # => True
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10 in filled_set # => False
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####################################################
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## 3. Control Flow
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# 3. Control Flow
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####################################################
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# Let's just make a variable
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@ -377,12 +375,11 @@ some_var = 5
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# prints "some_var is smaller than 10"
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if some_var > 10:
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print "some_var is totally bigger than 10."
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elif some_var < 10: # This elif clause is optional.
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elif some_var < 10: # This elif clause is optional.
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print "some_var is smaller than 10."
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else: # This is optional too.
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else: # This is optional too.
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print "some_var is indeed 10."
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"""
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For loops iterate over lists
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prints:
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@ -438,12 +435,12 @@ try:
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# Use "raise" to raise an error
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raise IndexError("This is an index error")
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except IndexError as e:
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pass # Pass is just a no-op. Usually you would do recovery here.
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pass # Pass is just a no-op. Usually you would do recovery here.
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except (TypeError, NameError):
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pass # Multiple exceptions can be handled together, if required.
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else: # Optional clause to the try/except block. Must follow all except blocks
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print "All good!" # Runs only if the code in try raises no exceptions
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finally: # Execute under all circumstances
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pass # Multiple exceptions can be handled together, if required.
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else: # Optional clause to the try/except block. Must follow all except blocks
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print "All good!" # Runs only if the code in try raises no exceptions
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finally: # Execute under all circumstances
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print "We can clean up resources here"
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# Instead of try/finally to cleanup resources you can use a with statement
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@ -453,19 +450,20 @@ with open("myfile.txt") as f:
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####################################################
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## 4. Functions
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# 4. Functions
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####################################################
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# Use "def" to create new functions
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def add(x, y):
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print "x is {0} and y is {1}".format(x, y)
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return x + y # Return values with a return statement
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return x + y # Return values with a return statement
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# Calling functions with parameters
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add(5, 6) # => prints out "x is 5 and y is 6" and returns 11
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add(5, 6) # => prints out "x is 5 and y is 6" and returns 11
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# Another way to call functions is with keyword arguments
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add(y=6, x=5) # Keyword arguments can arrive in any order.
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add(y=6, x=5) # Keyword arguments can arrive in any order.
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# You can define functions that take a variable number of
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@ -473,21 +471,26 @@ add(y=6, x=5) # Keyword arguments can arrive in any order.
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def varargs(*args):
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return args
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varargs(1, 2, 3) # => (1, 2, 3)
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varargs(1, 2, 3) # => (1, 2, 3)
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# You can define functions that take a variable number of
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# keyword args, as well, which will be interpreted as a dict by using **
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def keyword_args(**kwargs):
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return kwargs
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# Let's call it to see what happens
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keyword_args(big="foot", loch="ness") # => {"big": "foot", "loch": "ness"}
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keyword_args(big="foot", loch="ness") # => {"big": "foot", "loch": "ness"}
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# You can do both at once, if you like
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def all_the_args(*args, **kwargs):
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print args
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print kwargs
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"""
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all_the_args(1, 2, a=3, b=4) prints:
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(1, 2)
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@ -498,9 +501,10 @@ all_the_args(1, 2, a=3, b=4) prints:
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# Use * to expand positional args and use ** to expand keyword args.
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args = (1, 2, 3, 4)
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kwargs = {"a": 3, "b": 4}
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all_the_args(*args) # equivalent to foo(1, 2, 3, 4)
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all_the_args(**kwargs) # equivalent to foo(a=3, b=4)
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all_the_args(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4)
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all_the_args(*args) # equivalent to foo(1, 2, 3, 4)
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all_the_args(**kwargs) # equivalent to foo(a=3, b=4)
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all_the_args(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4)
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# you can pass args and kwargs along to other functions that take args/kwargs
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# by expanding them with * and ** respectively
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@ -509,58 +513,64 @@ def pass_all_the_args(*args, **kwargs):
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print varargs(*args)
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print keyword_args(**kwargs)
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# Function Scope
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x = 5
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def set_x(num):
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# Local var x not the same as global variable x
|
||||
x = num # => 43
|
||||
print x # => 43
|
||||
x = num # => 43
|
||||
print x # => 43
|
||||
|
||||
|
||||
def set_global_x(num):
|
||||
global x
|
||||
print x # => 5
|
||||
x = num # global var x is now set to 6
|
||||
print x # => 6
|
||||
print x # => 5
|
||||
x = num # global var x is now set to 6
|
||||
print x # => 6
|
||||
|
||||
|
||||
set_x(43)
|
||||
set_global_x(6)
|
||||
|
||||
|
||||
# Python has first class functions
|
||||
def create_adder(x):
|
||||
def adder(y):
|
||||
return x + y
|
||||
|
||||
return adder
|
||||
|
||||
|
||||
add_10 = create_adder(10)
|
||||
add_10(3) # => 13
|
||||
add_10(3) # => 13
|
||||
|
||||
# There are also anonymous functions
|
||||
(lambda x: x > 2)(3) # => True
|
||||
(lambda x, y: x ** 2 + y ** 2)(2, 1) # => 5
|
||||
(lambda x: x > 2)(3) # => True
|
||||
(lambda x, y: x ** 2 + y ** 2)(2, 1) # => 5
|
||||
|
||||
# There are built-in higher order functions
|
||||
map(add_10, [1, 2, 3]) # => [11, 12, 13]
|
||||
map(max, [1, 2, 3], [4, 2, 1]) # => [4, 2, 3]
|
||||
map(add_10, [1, 2, 3]) # => [11, 12, 13]
|
||||
map(max, [1, 2, 3], [4, 2, 1]) # => [4, 2, 3]
|
||||
|
||||
filter(lambda x: x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
|
||||
filter(lambda x: x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
|
||||
|
||||
# We can use list comprehensions for nice maps and filters
|
||||
[add_10(i) for i in [1, 2, 3]] # => [11, 12, 13]
|
||||
[x for x in [3, 4, 5, 6, 7] if x > 5] # => [6, 7]
|
||||
[x for x in [3, 4, 5, 6, 7] if x > 5] # => [6, 7]
|
||||
|
||||
# You can construct set and dict comprehensions as well.
|
||||
{x for x in 'abcddeef' if x in 'abc'} # => {'a', 'b', 'c'}
|
||||
{x: x**2 for x in range(5)} # => {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
|
||||
{x: x ** 2 for x in range(5)} # => {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
|
||||
|
||||
|
||||
####################################################
|
||||
## 5. Classes
|
||||
# 5. Classes
|
||||
####################################################
|
||||
|
||||
# We subclass from object to get a class.
|
||||
class Human(object):
|
||||
|
||||
# A class attribute. It is shared by all instances of this class
|
||||
species = "H. sapiens"
|
||||
|
||||
@ -575,7 +585,6 @@ class Human(object):
|
||||
# Initialize property
|
||||
self.age = 0
|
||||
|
||||
|
||||
# An instance method. All methods take "self" as the first argument
|
||||
def say(self, msg):
|
||||
return "{0}: {1}".format(self.name, msg)
|
||||
@ -611,45 +620,46 @@ class Human(object):
|
||||
|
||||
# Instantiate a class
|
||||
i = Human(name="Ian")
|
||||
print i.say("hi") # prints out "Ian: hi"
|
||||
print i.say("hi") # prints out "Ian: hi"
|
||||
|
||||
j = Human("Joel")
|
||||
print j.say("hello") # prints out "Joel: hello"
|
||||
|
||||
# Call our class method
|
||||
i.get_species() # => "H. sapiens"
|
||||
i.get_species() # => "H. sapiens"
|
||||
|
||||
# Change the shared attribute
|
||||
Human.species = "H. neanderthalensis"
|
||||
i.get_species() # => "H. neanderthalensis"
|
||||
j.get_species() # => "H. neanderthalensis"
|
||||
i.get_species() # => "H. neanderthalensis"
|
||||
j.get_species() # => "H. neanderthalensis"
|
||||
|
||||
# Call the static method
|
||||
Human.grunt() # => "*grunt*"
|
||||
Human.grunt() # => "*grunt*"
|
||||
|
||||
# Update the property
|
||||
i.age = 42
|
||||
|
||||
# Get the property
|
||||
i.age # => 42
|
||||
i.age # => 42
|
||||
|
||||
# Delete the property
|
||||
del i.age
|
||||
i.age # => raises an AttributeError
|
||||
|
||||
|
||||
####################################################
|
||||
## 6. Modules
|
||||
# 6. Modules
|
||||
####################################################
|
||||
|
||||
# You can import modules
|
||||
import math
|
||||
|
||||
print math.sqrt(16) # => 4
|
||||
|
||||
# You can get specific functions from a module
|
||||
from math import ceil, floor
|
||||
|
||||
print ceil(3.7) # => 4.0
|
||||
print floor(3.7) # => 3.0
|
||||
print floor(3.7) # => 3.0
|
||||
|
||||
# You can import all functions from a module.
|
||||
# Warning: this is not recommended
|
||||
@ -657,9 +667,11 @@ from math import *
|
||||
|
||||
# You can shorten module names
|
||||
import math as m
|
||||
math.sqrt(16) == m.sqrt(16) # => True
|
||||
|
||||
math.sqrt(16) == m.sqrt(16) # => True
|
||||
# you can also test that the functions are equivalent
|
||||
from math import sqrt
|
||||
|
||||
math.sqrt == m.sqrt == sqrt # => True
|
||||
|
||||
# Python modules are just ordinary python files. You
|
||||
@ -669,8 +681,10 @@ math.sqrt == m.sqrt == sqrt # => True
|
||||
# You can find out which functions and attributes
|
||||
# defines a module.
|
||||
import math
|
||||
|
||||
dir(math)
|
||||
|
||||
|
||||
# If you have a Python script named math.py in the same
|
||||
# folder as your current script, the file math.py will
|
||||
# be loaded instead of the built-in Python module.
|
||||
@ -679,7 +693,7 @@ dir(math)
|
||||
|
||||
|
||||
####################################################
|
||||
## 7. Advanced
|
||||
# 7. Advanced
|
||||
####################################################
|
||||
|
||||
# Generators
|
||||
@ -693,6 +707,7 @@ def double_numbers(iterable):
|
||||
for i in iterable:
|
||||
double_arr.append(i + i)
|
||||
|
||||
|
||||
# Running the following would mean we'll double all values first and return all
|
||||
# of them back to be checked by our condition
|
||||
for value in double_numbers(range(1000000)): # `test_non_generator`
|
||||
@ -700,12 +715,14 @@ for value in double_numbers(range(1000000)): # `test_non_generator`
|
||||
if value > 5:
|
||||
break
|
||||
|
||||
|
||||
# We could instead use a generator to "generate" the doubled value as the item
|
||||
# is being requested
|
||||
def double_numbers_generator(iterable):
|
||||
for i in iterable:
|
||||
yield i + i
|
||||
|
||||
|
||||
# Running the same code as before, but with a generator, now allows us to iterate
|
||||
# over the values and doubling them one by one as they are being consumed by
|
||||
# our logic. Hence as soon as we see a value > 5, we break out of the
|
||||
@ -723,22 +740,22 @@ for value in double_numbers_generator(xrange(1000000)): # `test_generator`
|
||||
|
||||
# Just as you can create a list comprehension, you can create generator
|
||||
# comprehensions as well.
|
||||
values = (-x for x in [1,2,3,4,5])
|
||||
values = (-x for x in [1, 2, 3, 4, 5])
|
||||
for x in values:
|
||||
print(x) # prints -1 -2 -3 -4 -5 to console/terminal
|
||||
|
||||
# You can also cast a generator comprehension directly to a list.
|
||||
values = (-x for x in [1,2,3,4,5])
|
||||
values = (-x for x in [1, 2, 3, 4, 5])
|
||||
gen_to_list = list(values)
|
||||
print(gen_to_list) # => [-1, -2, -3, -4, -5]
|
||||
|
||||
|
||||
# Decorators
|
||||
# in this example beg wraps say
|
||||
# Beg will call say. If say_please is True then it will change the returned
|
||||
# message
|
||||
from functools import wraps
|
||||
|
||||
|
||||
def beg(target_function):
|
||||
@wraps(target_function)
|
||||
def wrapper(*args, **kwargs):
|
||||
@ -749,11 +766,13 @@ def beg(target_function):
|
||||
|
||||
return wrapper
|
||||
|
||||
|
||||
@beg
|
||||
def say(say_please=False):
|
||||
msg = "Can you buy me a beer?"
|
||||
return msg, say_please
|
||||
|
||||
|
||||
print say() # Can you buy me a beer?
|
||||
print say(say_please=True) # Can you buy me a beer? Please! I am poor :(
|
||||
```
|
||||
|
||||
Loading…
Reference in New Issue
Block a user