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diff --git a/python.html.markdown b/python.html.markdown new file mode 100644 index 00000000..f69ffb14 --- /dev/null +++ b/python.html.markdown @@ -0,0 +1,1042 @@ +--- +language: python3 +contributors: + - ["Louie Dinh", "http://pythonpracticeprojects.com"] + - ["Steven Basart", "http://github.com/xksteven"] + - ["Andre Polykanine", "https://github.com/Oire"] + - ["Zachary Ferguson", "http://github.com/zfergus2"] + - ["evuez", "http://github.com/evuez"] + - ["Rommel Martinez", "https://ebzzry.io"] + - ["Roberto Fernandez Diaz", "https://github.com/robertofd1995"] + - ["caminsha", "https://github.com/caminsha"] +filename: learnpython3.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. + +Note: This article applies to Python 3 specifically. Check out [here](http://learnxinyminutes.com/docs/python/) if you want to learn the old Python 2.7 + +```python + +# Single line comments start with a number symbol. + +""" Multiline strings can be written + using three "s, and are often used + as documentation. +""" + +#################################################### +## 1. Primitive Datatypes and Operators +#################################################### + +# You have numbers +3 # => 3 + +# Math is what you would expect +1 + 1 # => 2 +8 - 1 # => 7 +10 * 2 # => 20 +35 / 5 # => 7.0 + +# Integer division rounds down for both positive and negative numbers. +5 // 3 # => 1 +-5 // 3 # => -2 +5.0 // 3.0 # => 1.0 # works on floats too +-5.0 // 3.0 # => -2.0 + +# The result of division is always a float +10.0 / 3 # => 3.3333333333333335 + +# Modulo operation +7 % 3 # => 1 + +# Exponentiation (x**y, x to the yth power) +2**3 # => 8 + +# Enforce precedence with parentheses +1 + 3 * 2 # => 7 +(1 + 3) * 2 # => 8 + +# Boolean values are primitives (Note: the capitalization) +True # => True +False # => False + +# negate with not +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 are actually 1 and 0 but with different keywords +True + True # => 2 +True * 8 # => 8 +False - 5 # => -5 + +# Comparison operators look at the numerical value of True and False +0 == False # => True +1 == True # => True +2 == True # => False +-5 != False # => 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 (&,|) +bool(0) # => False +bool(4) # => True +bool(-6) # => True +0 and 2 # => 0 +-5 or 0 # => -5 + +# Equality is == +1 == 1 # => True +2 == 1 # => False + +# Inequality is != +1 != 1 # => False +2 != 1 # => True + +# More comparisons +1 < 10 # => True +1 > 10 # => False +2 <= 2 # => True +2 >= 2 # => True + +# Seeing whether a value is in a range +1 < 2 and 2 < 3 # => True +2 < 3 and 3 < 2 # => False +# Chaining makes this look nicer +1 < 2 < 3 # => True +2 < 3 < 2 # => False + +# (is vs. ==) is checks if two variables 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 b 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." +'This is also a string.' + +# Strings can be added too! But try not to do this. +"Hello " + "world!" # => "Hello world!" +# String literals (but not variables) can be concatenated without using '+' +"Hello " "world!" # => "Hello world!" + +# A string can be treated like a list of characters +"This is a string"[0] # => 'T' + +# 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+) +name = "Reiko" +f"She said her name is {name}." # => "She said her name is Reiko" +# You can basically put any Python statement inside the braces and it will be output in the string. +f"{name} is {len(name)} characters long." # => "Reiko is 5 characters long." + + +# None is an object +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, 0, and empty strings/lists/dicts/tuples all evaluate to False. +# All other values are True +bool(0) # => False +bool("") # => False +bool([]) # => False +bool({}) # => False +bool(()) # => False + +#################################################### +## 2. Variables and Collections +#################################################### + +# Python has a print function +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 string. +print("Hello, World", end="!") # => Hello, World! + +# Simple way to get input data from console +input_string_var = input("Enter some data: ") # Returns the data as a string +# Note: In earlier versions of Python, input() method was named as raw_input() + +# There are no declarations, only assignments. +# Convention is to use lower_case_with_underscores +some_var = 5 +some_var # => 5 + +# Accessing a previously unassigned variable is an exception. +# See Control Flow to learn more about exception handling. +some_unknown_var # Raises a NameError + +# if can be used as an expression +# Equivalent of C's '?:' ternary operator +"yahoo!" if 3 > 2 else 2 # => "yahoo!" + +# Lists store sequences +li = [] +# You can start with a prefilled list +other_li = [4, 5, 6] + +# Add stuff to the end of a list with append +li.append(1) # li is now [1] +li.append(2) # li is now [1, 2] +li.append(4) # li is now [1, 2, 4] +li.append(3) # li is now [1, 2, 4, 3] +# Remove from the end with pop +li.pop() # => 3 and li is now [1, 2, 4] +# Let's put it back +li.append(3) # li is now [1, 2, 4, 3] again. + +# Access a list like you would any array +li[0] # => 1 +# Look at the last element +li[-1] # => 3 + +# Looking out of bounds is an IndexError +li[4] # Raises an IndexError + +# You can look at ranges with slice syntax. +# The start index is included, the end index is not +# (It's a closed/open range for you mathy types.) +li[1:3] # Return list from index 1 to 3 => [2, 4] +li[2:] # Return list starting from index 2 => [4, 3] +li[:3] # Return list from beginning until index 3 => [1, 2, 4] +li[::2] # Return list selecting every second entry => [1, 4] +li[::-1] # Return list in reverse order => [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. + +# Remove arbitrary elements from a list with "del" +del li[2] # li is now [1, 2, 3] + +# Remove first occurrence of a value +li.remove(2) # li is now [1, 3] +li.remove(2) # Raises a ValueError as 2 is not in the list + +# Insert an element at a specific index +li.insert(1, 2) # li is now [1, 2, 3] again + +# Get the index of the first item found matching the argument +li.index(2) # => 1 +li.index(4) # Raises a ValueError as 4 is not in the list + +# You can add lists +# Note: values for li and for other_li are not modified. +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] + +# Check for existence in a list with "in" +1 in li # => True + +# Examine the length with "len()" +len(li) # => 6 + + +# Tuples are like lists but are immutable. +tup = (1, 2, 3) +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'> + +# 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 + +# 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 +# You can also do extended unpacking +a, *b, c = (1, 2, 3, 4) # a is now 1, b is now [2, 3] and c is now 4 +# Tuples are created by default if you leave out the parentheses +d, e, f = 4, 5, 6 # tuple 4, 5, 6 is unpacked into variables d, e and f +# respectively such that d = 4, e = 5 and f = 6 +# Now look how easy it is to swap two values +e, d = d, e # d is now 5 and e is now 4 + + +# Dictionaries store mappings from keys to values +empty_dict = {} +# Here is a prefilled dictionary +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. + +# Look up values with [] +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 - for Python +# versions <3.7, dictionary key ordering is not guaranteed. Your results might +# not match the example below exactly. However, as of Python 3.7, dictionary +# items maintain the order at which they are inserted into the dictionary. +list(filled_dict.keys()) # => ["three", "two", "one"] in Python <3.7 +list(filled_dict.keys()) # => ["one", "two", "three"] in Python 3.7+ + + +# 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] in Python <3.7 +list(filled_dict.values()) # => [1, 2, 3] in Python 3.7+ + +# Check for existence of keys in a dictionary with "in" +"one" in filled_dict # => True +1 in filled_dict # => False + +# Looking up a non-existing key is a KeyError +filled_dict["four"] # KeyError + +# Use "get()" method to avoid the KeyError +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 + +# "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 + +# Remove keys from a dictionary with del +del filled_dict["one"] # Removes the key "one" from filled dict + +# From Python 3.5 you can also use the additional unpacking options +{'a': 1, **{'b': 2}} # => {'a': 1, 'b': 2} +{'a': 1, **{'a': 2}} # => {'a': 2} + + + +# 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} + +# Similar to keys of a dictionary, elements of a set have to be immutable. +invalid_set = {[1], 1} # => Raises a TypeError: unhashable type: 'list' +valid_set = {(1,), 1} + +# Add one more item to the set +filled_set = some_set +filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5} +# Sets do not have duplicate elements +filled_set.add(5) # it remains as before {1, 2, 3, 4, 5} + +# Do set intersection with & +other_set = {3, 4, 5, 6} +filled_set & other_set # => {3, 4, 5} + +# Do set union with | +filled_set | other_set # => {1, 2, 3, 4, 5, 6} + +# Do set difference with - +{1, 2, 3, 4} - {2, 3, 5} # => {1, 4} + +# Do set symmetric difference with ^ +{1, 2, 3, 4} ^ {2, 3, 5} # => {1, 4, 5} + +# Check if set on the left is a superset of set on the right +{1, 2} >= {1, 2, 3} # => False + +# Check if set on the left is a subset of set on the right +{1, 2} <= {1, 2, 3} # => True + +# Check for existence in a set with in +2 in filled_set # => True +10 in filled_set # => False + +# Make a one layer deep copy +filled_set = some_set.copy() # filled_set is {1, 2, 3, 4, 5} +filled_set is some_set # => False + + +#################################################### +## 3. Control Flow and Iterables +#################################################### + +# Let's just make a variable +some_var = 5 + +# Here is an if statement. Indentation is significant in Python! +# Convention is to use four spaces, not tabs. +# This prints "some_var is smaller than 10" +if some_var > 10: + print("some_var is totally bigger than 10.") +elif some_var < 10: # This elif clause is optional. + print("some_var is smaller than 10.") +else: # This is optional too. + print("some_var is indeed 10.") + + +""" +For loops iterate over lists +prints: + dog is a mammal + cat is a mammal + mouse is a mammal +""" +for animal in ["dog", "cat", "mouse"]: + # You can use format() to interpolate formatted strings + print("{} is a mammal".format(animal)) + +""" +"range(number)" returns an iterable of numbers +from zero to the given number +prints: + 0 + 1 + 2 + 3 +""" +for i in range(4): + print(i) + +""" +"range(lower, upper)" returns an iterable of numbers +from the lower number to the upper number +prints: + 4 + 5 + 6 + 7 +""" +for i in range(4, 8): + print(i) + +""" +"range(lower, upper, step)" returns an iterable of numbers +from the lower number to the upper number, while incrementing +by step. If step is not indicated, the default value is 1. +prints: + 4 + 6 +""" +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: + 0 dog + 1 cat + 2 mouse +""" +animals = ["dog", "cat", "mouse"] +for i, value in enumerate(animals): + print(i, value) + +""" +While loops go until a condition is no longer met. +prints: + 0 + 1 + 2 + 3 +""" +x = 0 +while x < 4: + print(x) + x += 1 # Shorthand for x = x + 1 + +# Handle exceptions with a try/except block +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. +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 + 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") + +# Instead of try/finally to cleanup resources you can use a with statement +with open("myfile.txt") as f: + for line in f: + print(line) + +# Writing to a file +contents = {"aa": 12, "bb": 21} +with open("myfile1.txt", "w+") as file: + file.write(str(contents)) # writes a string to a file + +with open("myfile2.txt", "w+") as file: + file.write(json.dumps(contents)) # writes an object to a file + +# Reading from a file +with open('myfile1.txt', "r+") as file: + contents = file.read() # reads a string from a file +print(contents) +# print: {"aa": 12, "bb": 21} + +with open('myfile2.txt', "r+") as file: + contents = json.load(file) # reads a json object from a file +print(contents) +# print: {"aa": 12, "bb": 21} + + +# Python offers a fundamental abstraction called the Iterable. +# An iterable is an object that can be treated as a sequence. +# The object returned by the range function, is an iterable. + +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. + +# We can loop over it. +for i in our_iterable: + print(i) # Prints one, two, three + +# However we cannot address elements by index. +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()". +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 +next(our_iterator) # Raises StopIteration + +# We can also loop over it, in fact, "for" does this implicitly! +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. +list(our_iterable) # => Returns ["one", "two", "three"] +list(our_iterator) # => Returns [] because state is saved + + +#################################################### +## 4. Functions +#################################################### + +# 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 + +# Calling functions with parameters +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. + +# You can define functions that take a variable number of +# positional arguments +def varargs(*args): + return args + +varargs(1, 2, 3) # => (1, 2, 3) + +# You can define functions that take a variable number of +# keyword arguments, as well +def keyword_args(**kwargs): + return kwargs + +# Let's call it to see what happens +keyword_args(big="foot", loch="ness") # => {"big": "foot", "loch": "ness"} + + +# You can do both at once, if you like +def all_the_args(*args, **kwargs): + print(args) + print(kwargs) +""" +all_the_args(1, 2, a=3, b=4) prints: + (1, 2) + {"a": 3, "b": 4} +""" + +# When calling functions, you can do the opposite of args/kwargs! +# 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) + +# 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) + +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. + +# Function Scope +x = 5 + +def set_x(num): + # Local var x not the same as global variable x + 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 + +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 + +# There are also anonymous functions +(lambda x: x > 2)(3) # => True +(lambda x, y: x ** 2 + y ** 2)(2, 1) # => 5 + +# There are built-in higher order functions +list(map(add_10, [1, 2, 3])) # => [11, 12, 13] +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 +[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] + +# You can construct set and dict comprehensions as well. +{x for x in 'abcddeef' if x not in 'abc'} # => {'d', 'e', 'f'} +{x: x**2 for x in range(5)} # => {0: 0, 1: 1, 2: 4, 3: 9, 4: 16} + + +#################################################### +## 5. Modules +#################################################### + +# You can import modules +import math +print(math.sqrt(16)) # => 4.0 + +# 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 + +# You can import all functions from a module. +# Warning: this is not recommended +from math import * + +# You can shorten module names +import math as m +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 +# module is the same as the name of the file. + +# You can find out which functions and attributes +# are defined in 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. +# This happens because the local folder has priority +# over Python's built-in libraries. + + +#################################################### +## 6. Classes +#################################################### + +# We use the "class" statement to create a class +class Human: + + # A class attribute. It is shared by all instances of this class + species = "H. sapiens" + + # Basic initializer, this is called when this class is instantiated. + # 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. + def __init__(self, name): + # Assign the argument to the instance's name attribute + self.name = name + + # Initialize property + self._age = 0 + + # An instance method. All methods take "self" as the first argument + def say(self, msg): + print("{name}: {message}".format(name=self.name, message=msg)) + + # Another instance method + def sing(self): + return 'yo... yo... microphone check... one two... one two...' + + # A class method is shared among all instances + # They are called with the calling class as the first argument + @classmethod + def get_species(cls): + return cls.species + + # A static method is called without a class or instance reference + @staticmethod + def grunt(): + return "*grunt*" + + # A property is just like a getter. + # It turns the method age() into an read-only attribute of the same name. + # There's no need to write trivial getters and setters in Python, though. + @property + def age(self): + return self._age + + # This allows the property to be set + @age.setter + def age(self, age): + self._age = age + + # This allows the property to be deleted + @age.deleter + def age(self): + del self._age + + +# When a Python interpreter reads a source file it executes all its code. +# This __name__ check makes sure this code block is only executed when this +# module is the main program. +if __name__ == '__main__': + # Instantiate a class + i = Human(name="Ian") + 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 + + # Call our class method + i.say(i.get_species()) # "Ian: H. sapiens" + # Change the shared attribute + Human.species = "H. neanderthalensis" + i.say(i.get_species()) # => "Ian: H. neanderthalensis" + j.say(j.get_species()) # => "Joel: H. neanderthalensis" + + # Call the static method + print(Human.grunt()) # => "*grunt*" + + # Cannot call static method with instance of object + # because i.grunt() will automatically put "self" (the object i) as an argument + print(i.grunt()) # => TypeError: grunt() takes 0 positional arguments but 1 was given + + # Update the property for this instance + i.age = 42 + # Get the property + i.say(i.age) # => "Ian: 42" + j.say(j.age) # => "Joel: 0" + # Delete the property + del i.age + # i.age # => this would raise an AttributeError + + +#################################################### +## 6.1 Inheritance +#################################################### + +# Inheritance allows new child classes to be defined that inherit methods and +# variables from their parent class. + +# Using the Human class defined above as the base or parent class, we can +# define a child class, Superhero, which inherits the class variables like +# "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 import functions from other files use the following format +# from "filename-without-extension" import "function-or-class" + +from human import Human + + +# Specify the parent class(es) as parameters to the class definition +class Superhero(Human): + + # If the child class should inherit all of the parent's definitions without + # any modifications, you can just use the "pass" keyword (and nothing else) + # but in this case it is commented out to allow for a unique child class: + # pass + + # Child classes can override their parents' attributes + species = 'Superhuman' + + # Children automatically inherit their parent class's constructor including + # its arguments, but can also define additional arguments or definitions + # and override its methods such as the class constructor. + # This constructor inherits the "name" argument from the "Human" class and + # adds the "superpower" and "movie" arguments: + def __init__(self, name, movie=False, + superpowers=["super strength", "bulletproofing"]): + + # add additional class attributes: + self.fictional = True + self.movie = movie + # be aware of mutable default values, since defaults are shared + self.superpowers = superpowers + + # The "super" function lets you access the parent class's methods + # that are overridden by the child, in this case, the __init__ method. + # This calls the parent class constructor: + super().__init__(name) + + # override the sing method + def sing(self): + return 'Dun, dun, DUN!' + + # add an additional instance method + def boast(self): + for power in self.superpowers: + print("I wield the power of {pow}!".format(pow=power)) + + +if __name__ == '__main__': + sup = Superhero(name="Tick") + + # Instance type checks + if isinstance(sup, Human): + print('I am human') + if type(sup) is Superhero: + print('I am a superhero') + + # Get the Method Resolution search Order used by both getattr() and super() + # This attribute is dynamic and can be updated + print(Superhero.__mro__) # => (<class '__main__.Superhero'>, + # => <class 'human.Human'>, <class 'object'>) + + # Calls parent method but uses its own class attribute + print(sup.get_species()) # => Superhuman + + # Calls overridden method + print(sup.sing()) # => Dun, dun, DUN! + + # Calls method from Human + sup.say('Spoon') # => Tick: Spoon + + # Call method that exists only in Superhero + sup.boast() # => I wield the power of super strength! + # => I wield the power of bulletproofing! + + # Inherited class attribute + sup.age = 31 + print(sup.age) # => 31 + + # Attribute that only exists within Superhero + print('Am I Oscar eligible? ' + str(sup.movie)) + +#################################################### +## 6.2 Multiple Inheritance +#################################################### + +# Another class definition +# bat.py +class Bat: + + species = 'Baty' + + def __init__(self, can_fly=True): + self.fly = can_fly + + # This class also has a say method + def say(self, msg): + msg = '... ... ...' + return msg + + # And its own method as well + def sonar(self): + return '))) ... (((' + +if __name__ == '__main__': + b = Bat() + print(b.say('hello')) + print(b.fly) + + +# And yet another class definition that inherits from Superhero and Bat +# superhero.py +from superhero import Superhero +from bat import Bat + +# Define Batman as a child that inherits from both Superhero and Bat +class Batman(Superhero, Bat): + + def __init__(self, *args, **kwargs): + # Typically to inherit attributes you have to call super: + # super(Batman, self).__init__(*args, **kwargs) + # 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". + Superhero.__init__(self, 'anonymous', movie=True, + superpowers=['Wealthy'], *args, **kwargs) + Bat.__init__(self, *args, can_fly=False, **kwargs) + # override the value for the name attribute + self.name = 'Sad Affleck' + + def sing(self): + return 'nan nan nan nan nan batman!' + + +if __name__ == '__main__': + sup = Batman() + + # Get the Method Resolution search Order used by both getattr() and super(). + # This attribute is dynamic and can be updated + print(Batman.__mro__) # => (<class '__main__.Batman'>, + # => <class 'superhero.Superhero'>, + # => <class 'human.Human'>, + # => <class 'bat.Bat'>, <class 'object'>) + + # Calls parent method but uses its own class attribute + print(sup.get_species()) # => Superhuman + + # Calls overridden method + print(sup.sing()) # => nan nan nan nan nan batman! + + # Calls method from Human, because inheritance order matters + sup.say('I agree') # => Sad Affleck: I agree + + # Call method that exists only in 2nd ancestor + print(sup.sonar()) # => ))) ... ((( + + # Inherited class attribute + sup.age = 100 + print(sup.age) # => 100 + + # Inherited attribute from 2nd ancestor whose default value was overridden. + print('Can I fly? ' + str(sup.fly)) # => Can I fly? False + + + +#################################################### +## 7. Advanced +#################################################### + +# Generators help you make lazy code. +def double_numbers(iterable): + for i in iterable: + yield i + i + +# Generators are memory-efficient because they only load the data needed to +# process the next value in the iterable. This allows them to perform +# operations on otherwise prohibitively large value ranges. +# NOTE: `range` replaces `xrange` in Python 3. +for i in double_numbers(range(1, 900000000)): # `range` is a generator. + print(i) + if i >= 30: + break + +# 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]) +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]) +gen_to_list = list(values) +print(gen_to_list) # => [-1, -2, -3, -4, -5] + + +# Decorators +# In this example `beg` wraps `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): + msg, say_please = target_function(*args, **kwargs) + if say_please: + return "{} {}".format(msg, "Please! I am poor :(") + return msg + + 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 :( +``` + +## Ready For More? + +### Free Online + +* [Automate the Boring Stuff with Python](https://automatetheboringstuff.com) +* [Ideas for Python Projects](http://pythonpracticeprojects.com) +* [The Official Docs](http://docs.python.org/3/) +* [Hitchhiker's Guide to Python](http://docs.python-guide.org/en/latest/) +* [Python Course](http://www.python-course.eu/index.php) +* [First Steps With Python](https://realpython.com/learn/python-first-steps/) +* [A curated list of awesome Python frameworks, libraries and software](https://github.com/vinta/awesome-python) +* [30 Python Language Features and Tricks You May Not Know About](http://sahandsaba.com/thirty-python-language-features-and-tricks-you-may-not-know.html) +* [Official Style Guide for Python](https://www.python.org/dev/peps/pep-0008/) +* [Python 3 Computer Science Circles](http://cscircles.cemc.uwaterloo.ca/) +* [Dive Into Python 3](http://www.diveintopython3.net/index.html) +* [A Crash Course in Python for Scientists](http://nbviewer.jupyter.org/gist/anonymous/5924718) |