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Diffstat (limited to 'python3.html.markdown')
| -rw-r--r-- | python3.html.markdown | 91 |
1 files changed, 66 insertions, 25 deletions
diff --git a/python3.html.markdown b/python3.html.markdown index b494dc1e..a112912f 100644 --- a/python3.html.markdown +++ b/python3.html.markdown @@ -3,23 +3,24 @@ language: python3 contributors: - ["Louie Dinh", "http://pythonpracticeprojects.com"] - ["Steven Basart", "http://github.com/xksteven"] + - ["Andre Polykanine", "https://github.com/Oire"] filename: learnpython3.py --- -Python was created by Guido Van Rossum in the early 90's. 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. Feedback would be highly appreciated! You can reach me at [@louiedinh](http://twitter.com/louiedinh) or louiedinh [at] [google's email service] -Note: This article applies to Python 3 specifically. Check out the other tutorial 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/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 + using three "s, and are often used as comments """ @@ -38,7 +39,7 @@ Note: This article applies to Python 3 specifically. Check out the other tutoria # Except division which returns floats by default 35 / 5 # => 7.0 -# Result of integer division truncated down both for positive and negative. +# 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 @@ -50,6 +51,9 @@ Note: This article applies to Python 3 specifically. Check out the other tutoria # Modulo operation 7 % 3 # => 1 +# Exponentiation (x to the yth power) +2**4 # => 16 + # Enforce precedence with parentheses (1 + 3) * 2 # => 8 @@ -61,6 +65,18 @@ False not True # => False not False # => True +# Boolean Operators +# Note "and" and "or" are case-sensitive +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 + # Equality is == 1 == 1 # => True 2 == 1 # => False @@ -85,6 +101,8 @@ not False # => True # 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!" # A string can be treated like a list of characters "This is a string"[0] # => 'T' @@ -93,7 +111,9 @@ not False # => True "{} can be {}".format("strings", "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" +"{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" + # 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" @@ -125,7 +145,8 @@ bool({}) #=> False # Python has a print function print("I'm Python. Nice to meet you!") -# No need to declare variables before assigning to them. Convention is to use lower_case_with_underscores +# No need to declare variables before assigning to them. +# Convention is to use lower_case_with_underscores some_var = 5 some_var # => 5 @@ -165,7 +186,7 @@ li[2:] # => [4, 3] li[:3] # => [1, 2, 4] # Select every second entry li[::2] # =>[1, 4] -# Revert the list +# Return a reversed copy of the list li[::-1] # => [3, 4, 2, 1] # Use any combination of these to make advanced slices # li[start:end:step] @@ -174,7 +195,8 @@ li[::-1] # => [3, 4, 2, 1] del li[2] # li is now [1, 2, 3] # You can add lists -li + other_li # => [1, 2, 3, 4, 5, 6] - Note: values for li and for other_li are not modified. +# 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] @@ -191,7 +213,7 @@ tup = (1, 2, 3) tup[0] # => 1 tup[0] = 3 # Raises a TypeError -# You can do all those list thingies on tuples too +# 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) @@ -213,14 +235,17 @@ filled_dict = {"one": 1, "two": 2, "three": 3} # Look up values with [] filled_dict["one"] # => 1 -# Get all keys as a list with "keys()". We need to wrap the call in list() because we are getting back an iterable. We'll talk about those later. +# 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"] -# Note - Dictionary key ordering is not guaranteed. -# Your results might not match this exactly. -# Get all values as a list with "values()". Once again we need to wrap it in list() to get it out of the iterable. + +# 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] -# Note - Same as above regarding key ordering. + # Check for existence of keys in a dictionary with "in" "one" in filled_dict # => True @@ -240,6 +265,10 @@ filled_dict.get("four", 4) # => 4 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 @@ -249,10 +278,10 @@ 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} -#Can set new variables to a set +# Can set new variables to a set filled_set = some_set -# Add one more item to the set +# Add one more item to the set filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5} # Do set intersection with & @@ -299,7 +328,7 @@ for animal in ["dog", "cat", "mouse"]: print("{} is a mammal".format(animal)) """ -"range(number)" returns a list of numbers +"range(number)" returns an iterable of numbers from zero to the given number prints: 0 @@ -311,6 +340,18 @@ 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) + +""" While loops go until a condition is no longer met. prints: 0 @@ -367,7 +408,6 @@ our_iterator.__next__() # Raises StopIteration list(filled_dict.keys()) #=> Returns ["one", "two", "three"] - #################################################### ## 4. Functions #################################################### @@ -383,7 +423,6 @@ 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): @@ -391,7 +430,6 @@ def varargs(*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): @@ -420,14 +458,14 @@ 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) -# Function Scope +# Function Scope x = 5 def setX(num): # Local var x not the same as global variable x x = num # => 43 print (x) # => 43 - + def setGlobalX(num): global x print (x) # => 5 @@ -456,6 +494,7 @@ map(add_10, [1, 2, 3]) # => [11, 12, 13] 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] @@ -473,7 +512,9 @@ class Human(object): # 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. You should not invent such names on your own. + # namespaces. Methods(or objects or attributes) like: __init__, __str__, + # __repr__ etc. are called magic 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 @@ -559,7 +600,7 @@ def double_numbers(iterable): # double_numbers. # Note range is a generator too. Creating a list 1-900000000 would take lot of # time to be made -# We use a trailing underscore in variable names when we want to use a name that +# We use a trailing underscore in variable names when we want to use a name that # would normally collide with a python keyword range_ = range(1, 900000000) # will double all numbers until a result >=30 found @@ -607,8 +648,8 @@ print(say(say_please=True)) # Can you buy me a beer? Please! I am poor :( * [The Official Docs](http://docs.python.org/3/) * [Hitchhiker's Guide to Python](http://docs.python-guide.org/en/latest/) -* [Python Module of the Week](http://pymotw.com/3/) * [A Crash Course in Python for Scientists](http://nbviewer.ipython.org/5920182) +* [Python Course](http://www.python-course.eu/index.php) ### Dead Tree |