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| -rw-r--r-- | python.html.markdown | 71 |
1 files changed, 37 insertions, 34 deletions
diff --git a/python.html.markdown b/python.html.markdown index 687529b5..2247f263 100644 --- a/python.html.markdown +++ b/python.html.markdown @@ -13,11 +13,13 @@ contributors: filename: learnpython.py --- -Python was created by Guido van Rossum in the early 90s. It is now one of the most popular -languages in existence. I fell in love with Python for its syntactic clarity. It's basically -executable pseudocode. +Python was created by Guido van Rossum in the early 90s. It is now one of the +most popular languages in existence. I fell in love with Python for its +syntactic clarity. It's basically executable pseudocode. -Note: This article applies to Python 3 specifically. Check out [here](http://learnxinyminutes.com/docs/pythonlegacy/) if you want to learn the old Python 2.7 +Note: This article applies to Python 3 specifically. Check out +[here](http://learnxinyminutes.com/docs/pythonlegacy/) if you want to learn the +old Python 2.7 ```python @@ -97,8 +99,9 @@ bool(set()) # => False bool(4) # => True bool(-6) # => True -# Using boolean logical operators on ints casts them to booleans for evaluation, but their non-cast value is returned -# Don't mix up with bool(ints) and bitwise and/or (&,|) +# Using boolean logical operators on ints casts them to booleans for evaluation, +# but their non-cast value is returned. Don't mix up with bool(ints) and bitwise +# and/or (&,|) bool(0) # => False bool(2) # => True 0 and 2 # => 0 @@ -152,10 +155,10 @@ b == a # => True, a's and b's objects are equal # You can find the length of a string len("This is a string") # => 16 -# You can also format using f-strings or formatted string literals (in Python 3.6+) +# Since Python 3.6, you can use f-strings or formatted string literals. name = "Reiko" f"She said her name is {name}." # => "She said her name is Reiko" -# You can basically put any Python expression inside the braces and it will be output in the string. +# Any valid Python expression inside these braces is returned to the string. f"{name} is {len(name)} characters long." # => "Reiko is 5 characters long." # None is an object @@ -294,7 +297,7 @@ 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' +invalid_dict = {[1,2,3]: "123"} # => Yield a TypeError: unhashable type: 'list' valid_dict = {(1,2,3):[1,2,3]} # Values can be of any type, however. # Look up values with [] @@ -348,7 +351,7 @@ 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. +# Initialize a set with a bunch of values. 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. @@ -454,8 +457,7 @@ for i in range(4, 8, 2): print(i) """ -To loop over a list, and retrieve both the index and the value of each item in the list -prints: +Loop over a list to retrieve both the index and the value of each list item: 0 dog 1 cat 2 mouse @@ -482,10 +484,11 @@ 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 # Refrain from this, provide a recovery (next example). 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 processed jointly. +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 print("We can clean up resources here") @@ -521,7 +524,8 @@ print(contents) filled_dict = {"one": 1, "two": 2, "three": 3} our_iterable = filled_dict.keys() -print(our_iterable) # => dict_keys(['one', 'two', 'three']). This is an object that implements our Iterable interface. +print(our_iterable) # => dict_keys(['one', 'two', 'three']). This is an object + # that implements our Iterable interface. # We can loop over it. for i in our_iterable: @@ -533,15 +537,16 @@ our_iterable[1] # Raises a TypeError # An iterable is an object that knows how to create an iterator. 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()". +# 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" # It maintains state as we iterate. next(our_iterator) # => "two" next(our_iterator) # => "three" -# After the iterator has returned all of its data, it raises a StopIteration exception +# After the iterator has returned all of its data, it raises a +# StopIteration exception next(our_iterator) # Raises StopIteration # We can also loop over it, in fact, "for" does this implicitly! @@ -549,7 +554,7 @@ our_iterator = iter(our_iterable) for i in our_iterator: print(i) # Prints one, two, three -# You can grab all the elements of an iterable or iterator by calling list() on it. +# You can grab all the elements of an iterable or iterator by call of list(). list(our_iterable) # => Returns ["one", "two", "three"] list(our_iterator) # => Returns [] because state is saved @@ -599,9 +604,9 @@ 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 all_the_args(1, 2, 3, 4) -all_the_args(**kwargs) # equivalent to all_the_args(a=3, b=4) -all_the_args(*args, **kwargs) # equivalent to all_the_args(1, 2, 3, 4, a=3, b=4) +all_the_args(*args) # equivalent: all_the_args(1, 2, 3, 4) +all_the_args(**kwargs) # equivalent: all_the_args(a=3, b=4) +all_the_args(*args, **kwargs) # equivalent: all_the_args(1, 2, 3, 4, a=3, b=4) # Returning multiple values (with tuple assignments) def swap(x, y): @@ -611,7 +616,7 @@ def swap(x, y): 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) # Again the use of parenthesis is optional. # global scope x = 5 @@ -659,7 +664,7 @@ list(map(max, [1, 2, 3], [4, 2, 1])) # => [4, 2, 3] list(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 +# List comprehension stores the output as a list (which itself may be nested). [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] @@ -719,8 +724,8 @@ class Human: # Note that the double leading and trailing underscores denote objects # or attributes that are used by Python but that live in user-controlled # namespaces. Methods(or objects or attributes) like: __init__, __str__, - # __repr__ etc. are called special methods (or sometimes called dunder methods) - # You should not invent such names on your own. + # __repr__ etc. are called special methods (or sometimes called dunder + # methods). You should not invent such names on your own. def __init__(self, name): # Assign the argument to the instance's name attribute self.name = name @@ -774,7 +779,7 @@ if __name__ == '__main__': i.say("hi") # "Ian: hi" j = Human("Joel") j.say("hello") # "Joel: hello" - # i and j are instances of type Human, or in other words: they are Human objects + # i and j are instances of type Human; i.e., they are Human objects. # Call our class method i.say(i.get_species()) # "Ian: H. sapiens" @@ -811,8 +816,8 @@ if __name__ == '__main__': # "species", "name", and "age", as well as methods, like "sing" and "grunt" # from the Human class, but can also have its own unique properties. -# To take advantage of modularization by file you could place the classes above in their own files, -# say, human.py +# To take advantage of modularization by file you could place the classes above +# in their own files, say, human.py # To import functions from other files use the following format # from "filename-without-extension" import "function-or-class" @@ -936,8 +941,8 @@ class Batman(Superhero, Bat): # However we are dealing with multiple inheritance here, and super() # only works with the next base class in the MRO list. # So instead we explicitly call __init__ for all ancestors. - # The use of *args and **kwargs allows for a clean way to pass arguments, - # with each parent "peeling a layer of the onion". + # The use of *args and **kwargs allows for a clean way to pass + # arguments, with each parent "peeling a layer of the onion". Superhero.__init__(self, 'anonymous', movie=True, superpowers=['Wealthy'], *args, **kwargs) Bat.__init__(self, *args, can_fly=False, **kwargs) @@ -1036,8 +1041,6 @@ print(say()) # Can you buy me a beer? print(say(say_please=True)) # Can you buy me a beer? Please! I am poor :( ``` -## Ready For More? - ### Free Online * [Automate the Boring Stuff with Python](https://automatetheboringstuff.com) |