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Diffstat (limited to 'python.html.markdown')
| -rw-r--r-- | python.html.markdown | 133 |
1 files changed, 93 insertions, 40 deletions
diff --git a/python.html.markdown b/python.html.markdown index 463556d9..e7ee6fbd 100644 --- a/python.html.markdown +++ b/python.html.markdown @@ -1,11 +1,12 @@ --- language: python -author: Louie Dinh -author_url: http://ldinh.ca +contributors: + - ["Louie Dinh", "http://ldinh.ca"] +filename: learnpython.py --- Python was created by Guido Van Rossum in the early 90's. It is now one of the most popular -languages in existence. I fell in love with Python for it's syntactic clarity. It's basically +languages in existence. I fell in love with Python for its syntactic clarity. Its 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] @@ -15,7 +16,7 @@ to Python 2.x. Look for another tour of Python 3 soon! ```python # Single line comments start with a hash. -""" Multiline strings can we written +""" Multiline strings can be written using three "'s, and are often used as comments """ @@ -86,10 +87,26 @@ not False #=> True # A newer way to format strings is the format method. # This method is the preferred way "{0} can be {1}".format("strings", "formatted") +# You can use keywords if you don't want to count. +"{name} wants to eat {food}".format(name="Bob", food="lasagna") # None is an object None #=> None +# Don't use the equality `==` symbol to compare objects to None +# Use `is` instead +"etc" is None #=> False +None is None #=> True + +# The 'is' operator tests for object identity. This isn't +# very useful when dealing with primitive values, but is +# very useful when dealing with objects. + +# None, 0, and empty strings/lists all evaluate to False. +# All other values are True +0 == False #=> True +"" == False #=> True + #################################################### ## 2. Variables and Collections @@ -103,16 +120,12 @@ print "I'm Python. Nice to meet you!" some_var = 5 # Convention is to use lower_case_with_underscores some_var #=> 5 -# Accessing a previously unassigned variable is an exception -try: - some_other_var -except NameError: - print "Raises a name error" +# Accessing a previously unassigned variable is an exception. +# See Control Flow to learn more about exception handling. +some_other_var # Raises a name error # if can be used as an expression -some_var = a if a > b else b -# If a is greater than b, then a is assigned to some_var. -# Otherwise b is assigned to some_var. +"yahoo!" if 3 > 2 else 2 #=> "yahoo!" # Lists store sequences li = [] @@ -135,10 +148,7 @@ li[0] #=> 1 li[-1] #=> 3 # Looking out of bounds is an IndexError -try: - li[4] # Raises an IndexError -except IndexError: - print "Raises an IndexError" +li[4] # Raises an IndexError # You can look at ranges with slice syntax. # (It's a closed/open range for you mathy types.) @@ -163,13 +173,11 @@ li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6] # Examine the length with len len(li) #=> 6 + # Tuples are like lists but are immutable. tup = (1, 2, 3) tup[0] #=> 1 -try: - tup[0] = 3 # Raises a TypeError -except TypeError: - print "Tuples cannot be mutated." +tup[0] = 3 # Raises a TypeError # You can do all those list thingies on tuples too len(tup) #=> 3 @@ -177,7 +185,7 @@ tup + (4, 5, 6) #=> (1, 2, 3, 4, 5, 6) tup[:2] #=> (1, 2) 2 in tup #=> True -# You can unpack tuples into variables +# 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 # Tuples are created by default if you leave out the parentheses d, e, f = 4, 5, 6 @@ -206,13 +214,12 @@ filled_dict.values() #=> [3, 2, 1] "one" in filled_dict #=> True 1 in filled_dict #=> False -# Trying to look up a non-existing key will raise a KeyError -filled_dict["four"] #=> KeyError + # 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 @@ -228,13 +235,13 @@ empty_set = set() some_set = set([1,2,2,3,4]) # filled_set is now set([1, 2, 3, 4]) # Since Python 2.7, {} can be used to declare a set -filled_set = {1 2 2 3 4} # => {1 2 3 4} +filled_set = {1, 2, 2, 3, 4} # => {1 2 3 4} # Add more items to a set filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5} # Do set intersection with & -other_set = set{3, 4, 5, 6} +other_set = {3, 4, 5, 6} filled_set & other_set #=> {3, 4, 5} # Do set union with | @@ -255,7 +262,7 @@ 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! +# Here is an if statement. Indentation is significant in python! # prints "some var is smaller than 10" if some_var > 10: print "some_var is totally bigger than 10." @@ -275,6 +282,18 @@ prints: for animal in ["dog", "cat", "mouse"]: # You can use % to interpolate formatted strings print "%s is a mammal" % animal + +""" +`range(number)` returns a list of numbers +from zero to the given number +prints: + 0 + 1 + 2 + 3 +""" +for i in range(4): + print i """ While loops go until a condition is no longer met. @@ -298,12 +317,6 @@ try: except IndexError as e: pass # Pass is just a no-op. Usually you would do recovery here. -# Works for Python 2.7 and down: -try: - raise IndexError("This is an index error") -except IndexError, e: # No "as", comma instead - pass - #################################################### ## 4. Functions @@ -315,7 +328,8 @@ def add(x, y): return x + y # Return values with a return statement # Calling functions with parameters -add(5, 6) #=> 11 and prints out "x is 5 and y is 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. @@ -341,16 +355,17 @@ def all_the_args(*args, **kwargs): print kwargs """ all_the_args(1, 2, a=3, b=4) prints: - [1, 2] + (1, 2) {"a": 3, "b": 4} """ -# You can also use * and ** when calling a function +# When calling functions, you can do the opposite of varargs/kwargs! +# Use * to expand tuples and use ** to expand kwargs. args = (1, 2, 3, 4) kwargs = {"a": 3, "b": 4} -foo(*args) # equivalent to foo(1, 2, 3, 4) -foo(**kwargs) # equivalent to foo(a=3, b=4) -foo(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4) +all_the_args(*args) # equivalent to foo(1, 2, 3, 4) +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) # Python has first class functions def create_adder(x): @@ -420,9 +435,47 @@ j.get_species() #=> "H. neanderthalensis" # Call the static method Human.grunt() #=> "*grunt*" + + +#################################################### +## 6. Modules +#################################################### + +# You can import modules +import math +print math.sqrt(16) #=> 4 + +# 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 +# defines a module. +import math +dir(math) + + ``` ## Further Reading -Still up for more? Try [Learn Python The Hard Way](http://learnpythonthehardway.org/book/) +Still up for more? Try: +* [Learn Python The Hard Way](http://learnpythonthehardway.org/book/) +* [Dive Into Python](http://www.diveintopython.net/) +* [The Official Docs](http://docs.python.org/2.6/) +* [Hitchhiker's Guide to Python](http://docs.python-guide.org/en/latest/) +* [Python Module of the Week](http://pymotw.com/2/) |