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some python keywords, which are in comments, enclosed in quotation marks to become clear (understandable)
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@ -158,19 +158,19 @@ li[2:] #=> [4, 3]
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# Omit the end
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li[:3] #=> [1, 2, 4]
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# Remove arbitrary elements from a list with del
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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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# You can add lists
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li + other_li #=> [1, 2, 3, 4, 5, 6] - Note: li and other_li is left alone
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# Concatenate lists with extend
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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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# Check for existence in a list with in
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# Check for existence in a list with `in`
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1 in li #=> True
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# Examine the length with len
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# Examine the length with `len()`
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len(li) #=> 6
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@ -201,37 +201,37 @@ 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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# Get all keys as a list
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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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# 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
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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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# Note - Same as above regarding key ordering.
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# Check for existence of keys in a dictionary with in
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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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# Looking up a non-existing key is a KeyError
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filled_dict["four"] # KeyError
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# Use get method to avoid the 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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# 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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# Setdefault method is a safe way to add new key-value pair into dictionary
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# `setdefault()` method is a safe way to add new key-value pair into dictionary
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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
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empty_set = set()
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# Initialize a set with a bunch of values
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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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# Since Python 2.7, {} can be used to declare a set
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@ -312,7 +312,7 @@ while x < 4:
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# Works on Python 2.6 and up:
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try:
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# Use raise to raise an error
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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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@ -322,7 +322,7 @@ except IndexError as e:
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## 4. Functions
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####################################################
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# Use def to create new functions
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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 %s and y is %s" % (x, y)
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return x + y # Return values with a return statement
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@ -359,7 +359,7 @@ all_the_args(1, 2, a=3, b=4) prints:
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{"a": 3, "b": 4}
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"""
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# When calling functions, you can do the opposite of varargs/kwargs!
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# When calling functions, you can do the opposite of args/kwargs!
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# Use * to expand tuples and use ** to expand kwargs.
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args = (1, 2, 3, 4)
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kwargs = {"a": 3, "b": 4}
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@ -402,7 +402,7 @@ class Human(object):
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# Assign the argument to the instance's name attribute
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self.name = name
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# An instance method. All methods take self as the first argument
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# An instance method. All methods take `self` as the first argument
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def say(self, msg):
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return "%s: %s" % (self.name, msg)
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