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Merge pull request #1504 from dillonjbyrne/patch-1

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[python3/en] Cleaned up formatting and clarified output
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Levi Bostian 2015-10-14 09:42:55 -05:00
commit ae4e4e81f4
1 changed files with 119 additions and 119 deletions
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@ -33,27 +33,27 @@ Note: This article applies to Python 3 specifically. Check out [here](http://lea
3 # => 3
# Math is what you would expect
1 + 1 # => 2
8 - 1 # => 7
1 + 1 # => 2
8 - 1 # => 7
10 * 2 # => 20
# Except division which returns floats, real numbers, by default
35 / 5 # => 7.0
# Result of integer division truncated down both for positive and negative.
5 // 3 # => 1
5.0 // 3.0 # => 1.0 # works on floats too
-5 // 3 # => -2
-5.0 // 3.0 # => -2.0
5 // 3 # => 1
5.0 // 3.0 # => 1.0 # works on floats too
-5 // 3 # => -2
-5.0 // 3.0 # => -2.0
# When you use a float, results are floats
3 * 2.0 # => 6.0
3 * 2.0 # => 6.0
# Modulo operation
7 % 3 # => 1
7 % 3 # => 1
# Exponentiation (x**y, x to the yth power)
2**4 # => 16
2**4 # => 16
# Enforce precedence with parentheses
(1 + 3) * 2 # => 8
@ -63,20 +63,20 @@ True
False
# negate with not
not True # => False
not True # => False
not False # => True
# Boolean Operators
# Note "and" and "or" are case-sensitive
True and False #=> False
False or True #=> True
True and False # => False
False or True # => True
# Note using Bool operators with ints
0 and 2 #=> 0
-5 or 0 #=> -5
0 == False #=> True
2 == True #=> False
1 == True #=> True
0 and 2 # => 0
-5 or 0 # => -5
0 == False # => True
2 == True # => False
1 == True # => True
# Equality is ==
1 == 1 # => True
@ -98,13 +98,13 @@ False or True #=> True
# (is vs. ==) is checks if two variable refer to the same object, but == checks
# if the objects pointed to have the same values.
a = [1, 2, 3, 4] # Point a at a new list, [1, 2, 3, 4]
b = a # Point b at what a is pointing to
b is a # => True, a and b refer to the same object
b == a # => True, a's and b's objects are equal
b = [1, 2, 3, 4] # Point a at a new list, [1, 2, 3, 4]
b is a # => False, a and b do not refer to the same object
b == a # => True, a's and b's objects are equal
a = [1, 2, 3, 4] # Point a at a new list, [1, 2, 3, 4]
b = a # Point b at what a is pointing to
b is a # => True, a and b refer to the same object
b == a # => True, a's and b's objects are equal
b = [1, 2, 3, 4] # Point a at a new list, [1, 2, 3, 4]
b is a # => False, a and b do not refer to the same object
b == a # => True, a's and b's objects are equal
# Strings are created with " or '
"This is a string."
@ -113,24 +113,24 @@ b == a # => True, a's and b's objects are equal
# Strings can be added too! But try not to do this.
"Hello " + "world!" # => "Hello world!"
# Strings can be added without using '+'
"Hello " "world!" # => "Hello world!"
"Hello " "world!" # => "Hello world!"
# A string can be treated like a list of characters
"This is a string"[0] # => 'T'
# .format can be used to format strings, like this:
"{} can be {}".format("strings", "interpolated")
"{} can be {}".format("Strings", "interpolated") # => "Strings can be interpolated"
# You can repeat the formatting arguments to save some typing.
"{0} be nimble, {0} be quick, {0} jump over the {1}".format("Jack", "candle stick")
#=> "Jack be nimble, Jack be quick, Jack jump over the candle stick"
# => "Jack be nimble, Jack be quick, Jack jump over the candle stick"
# You can use keywords if you don't want to count.
"{name} wants to eat {food}".format(name="Bob", food="lasagna") #=> "Bob wants to eat lasagna"
"{name} wants to eat {food}".format(name="Bob", food="lasagna") # => "Bob wants to eat lasagna"
# If your Python 3 code also needs to run on Python 2.5 and below, you can also
# still use the old style of formatting:
"%s can be %s the %s way" % ("strings", "interpolated", "old")
"%s can be %s the %s way" % ("Strings", "interpolated", "old") # => "Strings can be interpolated the old way"
# None is an object
@ -139,14 +139,14 @@ None # => None
# Don't use the equality "==" symbol to compare objects to None
# Use "is" instead. This checks for equality of object identity.
"etc" is None # => False
None is None # => True
None is None # => True
# None, 0, and empty strings/lists/dicts all evaluate to False.
# All other values are True
bool(0) # => False
bool(0) # => False
bool("") # => False
bool([]) #=> False
bool({}) #=> False
bool([]) # => False
bool({}) # => False
####################################################
@ -154,11 +154,11 @@ bool({}) #=> False
####################################################
# Python has a print function
print("I'm Python. Nice to meet you!")
print("I'm Python. Nice to meet you!") # => I'm Python. Nice to meet you!
# By default the print function also prints out a newline at the end.
# Use the optional argument end to change the end character.
print("Hello, World", end="!") # => Hello, World!
print("Hello, World", end="!") # => Hello, World!
# No need to declare variables before assigning to them.
# Convention is to use lower_case_with_underscores
@ -185,7 +185,7 @@ li.pop() # => 3 and li is now [1, 2, 4]
li.append(3) # li is now [1, 2, 4, 3] again.
# Access a list like you would any array
li[0] # => 1
li[0] # => 1
# Look at the last element
li[-1] # => 3
@ -194,61 +194,61 @@ li[4] # Raises an IndexError
# You can look at ranges with slice syntax.
# (It's a closed/open range for you mathy types.)
li[1:3] # => [2, 4]
li[1:3] # => [2, 4]
# Omit the beginning
li[2:] # => [4, 3]
li[2:] # => [4, 3]
# Omit the end
li[:3] # => [1, 2, 4]
li[:3] # => [1, 2, 4]
# Select every second entry
li[::2] # =>[1, 4]
# Return a reversed copy of the list
li[::-1] # => [3, 4, 2, 1]
li[::-1] # => [3, 4, 2, 1]
# Use any combination of these to make advanced slices
# li[start:end:step]
# Make a one layer deep copy using slices
li2 = li[:] # => li2 = [1, 2, 4, 3] but (li2 is li) will result in false.
li2 = li[:] # => li2 = [1, 2, 4, 3] but (li2 is li) will result in false.
# Remove arbitrary elements from a list with "del"
del li[2] # li is now [1, 2, 3]
del li[2] # li is now [1, 2, 3]
# You can add lists
# Note: values for li and for other_li are not modified.
li + other_li # => [1, 2, 3, 4, 5, 6]
li + other_li # => [1, 2, 3, 4, 5, 6]
# Concatenate lists with "extend()"
li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6]
li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6]
# Check for existence in a list with "in"
1 in li # => True
1 in li # => True
# Examine the length with "len()"
len(li) # => 6
len(li) # => 6
# Tuples are like lists but are immutable.
tup = (1, 2, 3)
tup[0] # => 1
tup[0] # => 1
tup[0] = 3 # Raises a TypeError
# Note that a tuple of length one has to have a comma after the last element but
# tuples of other lengths, even zero, do not.
type((1)) # => <class 'int'>
type((1,)) # => <class 'tuple'>
type(()) # => <class 'tuple'>
type((1)) # => <class 'int'>
type((1,)) # => <class 'tuple'>
type(()) # => <class 'tuple'>
# You can do most of the list operations on tuples too
len(tup) # => 3
tup + (4, 5, 6) # => (1, 2, 3, 4, 5, 6)
tup[:2] # => (1, 2)
2 in tup # => True
len(tup) # => 3
tup + (4, 5, 6) # => (1, 2, 3, 4, 5, 6)
tup[:2] # => (1, 2)
2 in tup # => True
# You can unpack tuples (or lists) into variables
a, b, c = (1, 2, 3) # a is now 1, b is now 2 and c is now 3
a, b, c = (1, 2, 3) # a is now 1, b is now 2 and c is now 3
# Tuples are created by default if you leave out the parentheses
d, e, f = 4, 5, 6
# Now look how easy it is to swap two values
e, d = d, e # d is now 5 and e is now 4
e, d = d, e # d is now 5 and e is now 4
# Dictionaries store mappings
@ -259,45 +259,45 @@ filled_dict = {"one": 1, "two": 2, "three": 3}
# Note keys for dictionaries have to be immutable types. This is to ensure that
# the key can be converted to a constant hash value for quick look-ups.
# Immutable types include ints, floats, strings, tuples.
invalid_dict = {[1,2,3]: "123"} # => Raises a TypeError: unhashable type: 'list'
valid_dict = {(1,2,3):[1,2,3]} # Values can be of any type, however.
invalid_dict = {[1,2,3]: "123"} # => Raises a TypeError: unhashable type: 'list'
valid_dict = {(1,2,3):[1,2,3]} # Values can be of any type, however.
# Look up values with []
filled_dict["one"] # => 1
filled_dict["one"] # => 1
# Get all keys as an iterable with "keys()". We need to wrap the call in list()
# to turn it into a list. We'll talk about those later. Note - Dictionary key
# ordering is not guaranteed. Your results might not match this exactly.
list(filled_dict.keys()) # => ["three", "two", "one"]
list(filled_dict.keys()) # => ["three", "two", "one"]
# Get all values as an iterable with "values()". Once again we need to wrap it
# in list() to get it out of the iterable. Note - Same as above regarding key
# ordering.
list(filled_dict.values()) # => [3, 2, 1]
list(filled_dict.values()) # => [3, 2, 1]
# Check for existence of keys in a dictionary with "in"
"one" in filled_dict # => True
1 in filled_dict # => False
"one" in filled_dict # => True
1 in filled_dict # => False
# Looking up a non-existing key is a KeyError
filled_dict["four"] # KeyError
filled_dict["four"] # KeyError
# Use "get()" method to avoid the KeyError
filled_dict.get("one") # => 1
filled_dict.get("four") # => None
filled_dict.get("one") # => 1
filled_dict.get("four") # => None
# The get method supports a default argument when the value is missing
filled_dict.get("one", 4) # => 1
filled_dict.get("four", 4) # => 4
filled_dict.get("four", 4) # => 4
# "setdefault()" inserts into a dictionary only if the given key isn't present
filled_dict.setdefault("five", 5) # filled_dict["five"] is set to 5
filled_dict.setdefault("five", 6) # filled_dict["five"] is still 5
# Adding to a dictionary
filled_dict.update({"four":4}) #=> {"one": 1, "two": 2, "three": 3, "four": 4}
#filled_dict["four"] = 4 #another way to add to dict
filled_dict.update({"four":4}) # => {"one": 1, "two": 2, "three": 3, "four": 4}
#filled_dict["four"] = 4 #another way to add to dict
# Remove keys from a dictionary with del
del filled_dict["one"] # Removes the key "one" from filled dict
@ -306,31 +306,31 @@ del filled_dict["one"] # Removes the key "one" from filled dict
# Sets store ... well sets
empty_set = set()
# Initialize a set with a bunch of values. Yeah, it looks a bit like a dict. Sorry.
some_set = {1, 1, 2, 2, 3, 4} # some_set is now {1, 2, 3, 4}
some_set = {1, 1, 2, 2, 3, 4} # some_set is now {1, 2, 3, 4}
# Similar to keys of a dictionary, elements of a set have to be immutable.
invalid_set = {[1], 1} # => Raises a TypeError: unhashable type: 'list'
invalid_set = {[1], 1} # => Raises a TypeError: unhashable type: 'list'
valid_set = {(1,), 1}
# Can set new variables to a set
filled_set = some_set
# Add one more item to the set
filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5}
filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5}
# Do set intersection with &
other_set = {3, 4, 5, 6}
filled_set & other_set # => {3, 4, 5}
filled_set & other_set # => {3, 4, 5}
# Do set union with |
filled_set | other_set # => {1, 2, 3, 4, 5, 6}
filled_set | other_set # => {1, 2, 3, 4, 5, 6}
# Do set difference with -
{1, 2, 3, 4} - {2, 3, 5} # => {1, 4}
{1, 2, 3, 4} - {2, 3, 5} # => {1, 4}
# Check for existence in a set with in
2 in filled_set # => True
10 in filled_set # => False
10 in filled_set # => False
@ -416,12 +416,12 @@ try:
# Use "raise" to raise an error
raise IndexError("This is an index error")
except IndexError as e:
pass # Pass is just a no-op. Usually you would do recovery here.
pass # Pass is just a no-op. Usually you would do recovery here.
except (TypeError, NameError):
pass # Multiple exceptions can be handled together, if required.
else: # Optional clause to the try/except block. Must follow all except blocks
pass # Multiple exceptions can be handled together, if required.
else: # Optional clause to the try/except block. Must follow all except blocks
print("All good!") # Runs only if the code in try raises no exceptions
finally: # Execute under all circumstances
finally: # Execute under all circumstances
print("We can clean up resources here")
# Instead of try/finally to cleanup resources you can use a with statement
@ -435,11 +435,11 @@ with open("myfile.txt") as f:
filled_dict = {"one": 1, "two": 2, "three": 3}
our_iterable = filled_dict.keys()
print(our_iterable) #=> range(1,10). This is an object that implements our Iterable interface
print(our_iterable) # => range(1,10). This is an object that implements our Iterable interface
# We can loop over it.
for i in our_iterable:
print(i) # Prints one, two, three
print(i) # Prints one, two, three
# However we cannot address elements by index.
our_iterable[1] # Raises a TypeError
@ -449,17 +449,17 @@ our_iterator = iter(our_iterable)
# Our iterator is an object that can remember the state as we traverse through it.
# We get the next object with "next()".
next(our_iterator) #=> "one"
next(our_iterator) # => "one"
# It maintains state as we iterate.
next(our_iterator) #=> "two"
next(our_iterator) #=> "three"
next(our_iterator) # => "two"
next(our_iterator) # => "three"
# After the iterator has returned all of its data, it gives you a StopIterator Exception
next(our_iterator) # Raises StopIteration
next(our_iterator) # Raises StopIteration
# You can grab all the elements of an iterator by calling list() on it.
list(filled_dict.keys()) #=> Returns ["one", "two", "three"]
list(filled_dict.keys()) # => Returns ["one", "two", "three"]
####################################################
@ -469,20 +469,20 @@ list(filled_dict.keys()) #=> Returns ["one", "two", "three"]
# Use "def" to create new functions
def add(x, y):
print("x is {} and y is {}".format(x, y))
return x + y # Return values with a return statement
return x + y # Return values with a return statement
# Calling functions with parameters
add(5, 6) # => prints out "x is 5 and y is 6" and returns 11
add(5, 6) # => prints out "x is 5 and y is 6" and returns 11
# Another way to call functions is with keyword arguments
add(y=6, x=5) # Keyword arguments can arrive in any order.
add(y=6, x=5) # Keyword arguments can arrive in any order.
# You can define functions that take a variable number of
# positional arguments
def varargs(*args):
return args
varargs(1, 2, 3) # => (1, 2, 3)
varargs(1, 2, 3) # => (1, 2, 3)
# You can define functions that take a variable number of
# keyword arguments, as well
@ -490,7 +490,7 @@ def keyword_args(**kwargs):
return kwargs
# Let's call it to see what happens
keyword_args(big="foot", loch="ness") # => {"big": "foot", "loch": "ness"}
keyword_args(big="foot", loch="ness") # => {"big": "foot", "loch": "ness"}
# You can do both at once, if you like
@ -507,33 +507,33 @@ all_the_args(1, 2, a=3, b=4) prints:
# Use * to expand tuples and use ** to expand kwargs.
args = (1, 2, 3, 4)
kwargs = {"a": 3, "b": 4}
all_the_args(*args) # equivalent to foo(1, 2, 3, 4)
all_the_args(**kwargs) # equivalent to foo(a=3, b=4)
all_the_args(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4)
all_the_args(*args) # equivalent to foo(1, 2, 3, 4)
all_the_args(**kwargs) # equivalent to foo(a=3, b=4)
all_the_args(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4)
# Returning multiple values (with tuple assignments)
def swap(x, y):
return y, x # Return multiple values as a tuple without the parenthesis.
# (Note: parenthesis have been excluded but can be included)
return y, x # Return multiple values as a tuple without the parenthesis.
# (Note: parenthesis have been excluded but can be included)
x = 1
y = 2
x, y = swap(x, y) # => x = 2, y = 1
# (x, y) = swap(x,y) # Again parenthesis have been excluded but can be included.
x, y = swap(x, y) # => x = 2, y = 1
# (x, y) = swap(x,y) # Again parenthesis have been excluded but can be included.
# Function Scope
x = 5
def setX(num):
# Local var x not the same as global variable x
x = num # => 43
print (x) # => 43
x = num # => 43
print (x) # => 43
def setGlobalX(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
setX(43)
setGlobalX(6)
@ -549,20 +549,20 @@ add_10 = create_adder(10)
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
# TODO - Fix for iterables
# 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
# List comprehension stores the output as a list which can itself be a nested list
[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]
[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]
####################################################
## 5. Classes
@ -609,15 +609,15 @@ 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*"
####################################################
@ -630,8 +630,8 @@ 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(ceil(3.7)) # => 4.0
print(floor(3.7)) # => 3.0
# You can import all functions from a module.
# Warning: this is not recommended
@ -639,7 +639,7 @@ 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
# Python modules are just ordinary python files. You
# can write your own, and import them. The name of the
@ -698,7 +698,7 @@ def say(say_please=False):
return msg, say_please
print(say()) # Can you buy me a beer?
print(say()) # Can you buy me a beer?
print(say(say_please=True)) # Can you buy me a beer? Please! I am poor :(
```