From 9ccd1ee05ade8f2b76d8c473f34695b775330d31 Mon Sep 17 00:00:00 2001 From: Ned Batchelder Date: Thu, 18 May 2017 06:40:25 -0400 Subject: Some improvements to Python 3 (#2713) --- python3.html.markdown | 49 ++++++++++++++++++++++++------------------------- 1 file changed, 24 insertions(+), 25 deletions(-) diff --git a/python3.html.markdown b/python3.html.markdown index cb53eaf8..f25d9228 100644 --- a/python3.html.markdown +++ b/python3.html.markdown @@ -9,7 +9,7 @@ contributors: filename: learnpython3.py --- -Python was created by Guido Van Rossum in the early 90s. It is now one of the most popular +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. @@ -23,7 +23,7 @@ Note: This article applies to Python 3 specifically. Check out [here](http://lea """ Multiline strings can be written using three "s, and are often used - as comments + as documentation. """ #################################################### @@ -114,7 +114,7 @@ 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 '+' +# String literals (but not variables) can be concatenated without using '+' "Hello " "world!" # => "Hello world!" # A string can be treated like a list of characters @@ -162,14 +162,14 @@ bool(()) # => False 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. +# 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() -# No need to declare variables before assigning to them. +# There are no declarations, only assignments. # Convention is to use lower_case_with_underscores some_var = 5 some_var # => 5 @@ -206,6 +206,7 @@ li[-1] # => 3 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] # => [2, 4] # Omit the end @@ -277,7 +278,7 @@ d, e, f = 4, 5, 6 e, d = d, e # d is now 5 and e is now 4 -# Dictionaries store mappings +# Dictionaries store mappings from keys to values empty_dict = {} # Here is a prefilled dictionary filled_dict = {"one": 1, "two": 2, "three": 3} @@ -323,7 +324,7 @@ 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["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 @@ -343,9 +344,6 @@ some_set = {1, 1, 2, 2, 3, 4} # some_set is now {1, 2, 3, 4} 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} @@ -381,8 +379,9 @@ filled_set | other_set # => {1, 2, 3, 4, 5, 6} # Let's just make a variable some_var = 5 -# Here is an if statement. Indentation is significant in python! -# prints "some_var is smaller than 10" +# 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. @@ -470,7 +469,7 @@ with open("myfile.txt") as f: # Python offers a fundamental abstraction called the Iterable. # An iterable is an object that can be treated as a sequence. -# The object returned the range function, is an iterable. +# The object returned by the range function, is an iterable. filled_dict = {"one": 1, "two": 2, "three": 3} our_iterable = filled_dict.keys() @@ -494,7 +493,7 @@ next(our_iterator) # => "one" next(our_iterator) # => "two" next(our_iterator) # => "three" -# After the iterator has returned all of its data, it gives you a StopIteration Exception +# After the iterator has returned all of its data, it raises a StopIteration exception next(our_iterator) # Raises StopIteration # You can grab all the elements of an iterator by calling list() on it. @@ -566,13 +565,13 @@ x = 5 def set_x(num): # Local var x not the same as global variable x x = num # => 43 - print (x) # => 43 + print(x) # => 43 def set_global_x(num): global x - print (x) # => 5 + print(x) # => 5 x = num # global var x is now set to 6 - print (x) # => 6 + print(x) # => 6 set_x(43) set_global_x(6) @@ -628,12 +627,12 @@ from math import * import math as m math.sqrt(16) == m.sqrt(16) # => True -# Python modules are just ordinary python files. You +# 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 -# defines a module. +# are defined in a module. import math dir(math) @@ -648,7 +647,7 @@ dir(math) ## 6. Classes #################################################### -# We use the "class" operator to get a class +# We use the "class" statement to create a class class Human: # A class attribute. It is shared by all instances of this class @@ -656,9 +655,9 @@ class Human: # 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 + # 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 magic methods (or sometimes called dunder methods) + # __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 @@ -687,8 +686,8 @@ class Human: return "*grunt*" # A property is just like a getter. - # It turns the method age() into an read-only attribute - # of the same name. + # 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 @@ -768,7 +767,7 @@ if __name__ == '__main__': # To take advantage of modularization by file you could place the classes above in their own files, # say, human.py and bat.py -# to import functions from other files use the following format +# To import functions from other files use the following format # from "filename-without-extension" import "function-or-class" # superhero.py -- cgit v1.2.3