summaryrefslogtreecommitdiffhomepage
path: root/python.html.markdown
diff options
context:
space:
mode:
Diffstat (limited to 'python.html.markdown')
-rw-r--r--python.html.markdown84
1 files changed, 62 insertions, 22 deletions
diff --git a/python.html.markdown b/python.html.markdown
index 9057dde2..53381f32 100644
--- a/python.html.markdown
+++ b/python.html.markdown
@@ -3,24 +3,25 @@ language: python
contributors:
- ["Louie Dinh", "http://ldinh.ca"]
- ["Amin Bandali", "http://aminbandali.com"]
+ - ["Andre Polykanine", "https://github.com/Oire"]
filename: learnpython.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 2.7 specifically, but should be applicable
-to Python 2.x. Look for another tour of Python 3 soon!
+to Python 2.x. For Python 3.x, take a look at the Python 3 tutorial.
```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
"""
@@ -54,12 +55,23 @@ to Python 2.x. Look for another tour of Python 3 soon!
# Modulo operation
7 % 3 # => 1
+# Exponentiation (x to the yth power)
+2**4 # => 16
+
# Enforce precedence with parentheses
(1 + 3) * 2 # => 8
-# Boolean values are primitives
-True
-False
+# 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
# negate with not
not True # => False
@@ -90,6 +102,9 @@ not False # => True
# Strings can be added too!
"Hello " + "world!" # => "Hello world!"
+# ... or multiplied
+"Hello" * 3 # => "HelloHelloHello"
+
# A string can be treated like a list of characters
"This is a string"[0] # => 'T'
@@ -124,11 +139,12 @@ bool("") # => False
## 2. Variables and Collections
####################################################
-# Python has a print function, available in versions 2.7 and 3...
-print("I'm Python. Nice to meet you!")
-# and an older print statement, in all 2.x versions but removed from 3.
-print "I'm also Python!"
-
+# Python has a print statement, in all 2.x versions but removed from 3.
+print "I'm Python. Nice to meet you!"
+# Python also has a print function, available in versions 2.7 and 3...
+# but for 2.7 you need to add the import (uncommented):
+# from __future__ import print_function
+print("I'm also Python! ")
# No need to declare variables before assigning to them.
some_var = 5 # Convention is to use lower_case_with_underscores
@@ -158,6 +174,10 @@ li.append(3) # li is now [1, 2, 4, 3] again.
# Access a list like you would any array
li[0] # => 1
+# Assign new values to indexes that have already been initialized with =
+li[0] = 42
+li[0] # => 42
+li[0] = 1 # Note: setting it back to the original value
# Look at the last element
li[-1] # => 3
@@ -182,7 +202,8 @@ 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.
+li + other_li # => [1, 2, 3, 4, 5, 6]
+# Note: values for li and for other_li are not modified.
# Concatenate lists with "extend()"
li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6]
@@ -243,17 +264,25 @@ 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
+# note that filled_dict.get("four") is still => 4
+# (get doesn't set the value in the dictionary)
+
+# set the value of a key with a syntax similar to lists
+filled_dict["four"] = 4 # now, filled_dict["four"] => 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
-# Sets store ... well sets
+# Sets store ... well sets (which are like lists but can contain no duplicates)
empty_set = set()
# Initialize a "set()" with a bunch of values
some_set = set([1, 2, 2, 3, 4]) # some_set is now set([1, 2, 3, 4])
+# order is not guaranteed, even though it may sometimes look sorted
+another_set = set([4, 3, 2, 2, 1]) # another_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}
@@ -359,7 +388,7 @@ add(y=6, x=5) # Keyword arguments can arrive in any order.
# You can define functions that take a variable number of
-# positional arguments
+# positional args, which will be interpreted as a tuple if you do not use the *
def varargs(*args):
return args
@@ -367,7 +396,7 @@ varargs(1, 2, 3) # => (1, 2, 3)
# You can define functions that take a variable number of
-# keyword arguments, as well
+# keyword args, as well, which will be interpreted as a map if you do not use **
def keyword_args(**kwargs):
return kwargs
@@ -386,26 +415,33 @@ all_the_args(1, 2, a=3, b=4) prints:
"""
# When calling functions, you can do the opposite of args/kwargs!
-# Use * to expand tuples and use ** to expand kwargs.
+# Use * to expand positional args and use ** to expand keyword args.
args = (1, 2, 3, 4)
kwargs = {"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)
+# you can pass args and kwargs along to other functions that take args/kwargs
+# by expanding them with * and ** respectively
+def pass_all_the_args(*args, **kwargs):
+ all_the_args(*args, **kwargs)
+ print varargs(*args)
+ print keyword_args(**kwargs)
+
# Function Scope
x = 5
def setX(num):
# Local var x not the same as global variable x
x = num # => 43
- print (x) # => 43
+ print x # => 43
def setGlobalX(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
setX(43)
setGlobalX(6)
@@ -430,11 +466,11 @@ filter(lambda x: x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
[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]
+
####################################################
## 5. Classes
####################################################
-
# We subclass from object to get a class.
class Human(object):
@@ -504,6 +540,9 @@ from math import *
# You can shorten module names
import math as m
math.sqrt(16) == m.sqrt(16) # => True
+# you can also test that the functions are equivalent
+from math import sqrt
+math.sqrt == m.sqrt == sqrt # => True
# Python modules are just ordinary python files. You
# can write your own, and import them. The name of the
@@ -530,8 +569,9 @@ def double_numbers(iterable):
# double_numbers.
# Note xrange is a generator that does the same thing range does.
# Creating a list 1-900000000 would take lot of time and space to be made.
-# xrange creates an xrange generator object instead of creating the entire list like range does.
-# We use a trailing underscore in variable names when we want to use a name that
+# xrange creates an xrange generator object instead of creating the entire list
+# like range does.
+# We use a trailing underscore in variable names when we want to use a name that
# would normally collide with a python keyword
xrange_ = xrange(1, 900000000)