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diff --git a/python.html.markdown b/python.html.markdown
index 982333ca..e0851950 100644
--- a/python.html.markdown
+++ b/python.html.markdown
@@ -2,19 +2,23 @@
language: python
author: Louie Dinh
author_url: 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
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!
```python
# Single line comments start with a hash.
-""" Multiline comments can we written
- using three "'s
+""" Multiline strings can be written
+ using three "'s, and are often used
+ as comments
"""
####################################################
@@ -32,11 +36,11 @@ to Python 2.x. Look for another tour of Python 3 soon!
# Division is a bit tricky. It is integer division and floors the results
# automatically.
-11 / 4 #=> 2
+5 / 2 #=> 2
# To fix division we need to learn about floats.
2.0 # This is a float
-5.0 / 2.0 #=> 2.5 ahhh...much better
+11.0 / 4.0 #=> 2.75 ahhh...much better
# Enforce precedence with parentheses
(1 + 3) * 2 #=> 8
@@ -77,9 +81,32 @@ not False #=> True
# A string can be treated like a list of characters
"This is a string"[0] #=> 'T'
+# % can be used to format strings, like this:
+"%s can be %s" % ("strings", "interpolated")
+
+# 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
@@ -93,16 +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
-# Conditional Expressions can be used when assigning
-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.
+# if can be used as an expression
+"yahoo!" if 3 > 2 else 2 #=> "yahoo!"
# Lists store sequences
li = []
@@ -122,21 +145,18 @@ 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] #=> 4
+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.)
li[1:3] #=> [2, 4]
# Omit the beginning
-li[:3] #=> [1, 2, 4]
-# Omit the end
li[2:] #=> [4, 3]
+# Omit the end
+li[:3] #=> [1, 2, 4]
# Remove arbitrary elements from a list with del
del li[2] # li is now [1, 2, 3]
@@ -145,7 +165,7 @@ del li[2] # li is now [1, 2, 3]
li + other_li #=> [1, 2, 3, 4, 5, 6] - Note: li and other_li is left alone
# Concatenate lists with extend
-li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6]
+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
@@ -153,13 +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
@@ -167,7 +185,7 @@ tup + (4, 5, 6) #=> (1, 2, 3, 4, 5, 6)
tup[:2] #=> (1, 2)
2 in tup #=> True
-# However, 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
@@ -196,10 +214,13 @@ 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
@@ -211,18 +232,23 @@ filled_dict.setdefault("five", 6) #filled_dict["five"] is still 5
# Sets store ... well sets
empty_set = set()
# Initialize a set with a bunch of values
-filled_set = set([1,2,2,3,4]) # filled_set is now set([1, 2, 3, 4])
+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}
# Add more items to a set
-filled_set.add(5) # filled_set is now set([1, 2, 3, 4, 5])
+filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5}
# Do set intersection with &
-other_set = set([3, 4, 5 ,6])
-filled_set & other_set #=> set([3, 4, 5])
+other_set = {3, 4, 5, 6}
+filled_set & other_set #=> {3, 4, 5}
+
# Do set union with |
-filled_set | other_set #=> set([1, 2, 3, 4, 5, 6])
+filled_set | other_set #=> {1, 2, 3, 4, 5, 6}
+
# Do set difference with -
-set([1,2,3,4]) - set([2,3,5]) #=> set([1, 4])
+{1,2,3,4} - {2,3,5} #=> {1, 4}
# Check for existence in a set with in
2 in filled_set #=> True
@@ -236,7 +262,7 @@ set([1,2,3,4]) - set([2,3,5]) #=> set([1, 4])
# 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."
@@ -255,14 +281,26 @@ prints:
"""
for animal in ["dog", "cat", "mouse"]:
# You can use % to interpolate formatted strings
- print "%s is a mammal" % animal
+ 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.
prints:
0
1
- 2
+ 2
3
"""
x = 0
@@ -279,12 +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
@@ -296,7 +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.
@@ -322,16 +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):
@@ -395,11 +429,53 @@ print j.say("hello") #prints out "Joel: hello"
i.get_species() #=> "H. sapiens"
# Change the shared attribute
-i.species = "H. neanderthalensis"
+Human.species = "H. neanderthalensis"
i.get_species() #=> "H. neanderthalensis"
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/)
+* [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/)