from IPython.core.display import Image 
Image(url='http://labrosa.ee.columbia.edu/crucialpython/logo.png', width=600) 

a_list = ['hey', [1, 2, 3], 2, 10, {}]
for item in a_list:
    print item

# Another example of an iterator is a file
with open('some_file.txt', 'r') as f:
    for line in f:
        print line

a_dict = {}
# This is kind of ugly and only works for objects with a len
for n in xrange(len(a_list)):
    if isinstance(a_list[n], int):
        a_dict[n] = n*a_list[n]
# You know about pprint (pretty print), right?
import pprint
pprint.pprint(a_dict)

# file objects don't have a len() because they are not loaded into memory.
# But, you can still use enumerate, which will give you an index.
# Plus, it's cleaner.
for n, item in enumerate(open('some_file.txt', 'r')):
    a_dict[n + 5] = item
pprint.pprint(a_dict)

b_list = ['cool', 'great', 'awesome', 'nice', 'sweet']
c_list = range(10, 15)
# Naw
for n in xrange(len(a_list)):
    print n, a_list[n], b_list[n], c_list[n]

# Yeah
for a_item, b_item, c_item in zip(a_list, b_list, c_list):
    print a_item, b_item, c_item

# When you need indices and items across lists, enumerate and zip!
for n, (a_item, b_item, c_item) in enumerate(zip(a_list, b_list, c_list)):
    print n, a_item, b_item, c_item

import itertools

# We can add lists to concatenate them, but we can't add list + file.
# Plus, we don't know how many items the file has in it.
# Chain lets us iterate over file first, then the list.
# We could do this in two for loops, but then we'd have to duplicate code.
for item in itertools.chain(open('some_file.txt', 'r'), a_list):
    print item

# Zip for things of different length
for a, b in itertools.izip(a_list, open('some_file.txt', 'r')):
    print a, b

for a, b in itertools.izip_longest(a_list, open('some_file.txt', 'r')):
    print a, b

short_list = ['dang', 'cool', 'nice']
# Get all length-n combinations of items from the list, ordered
for item_a, item_b in itertools.permutations(short_list, 2):
    print item_a, item_b

# Get all length-n combinations of items from the list, no repeats
for item_a, item_b in itertools.combinations(short_list, 2):
    print item_a, item_b

# Basic example: Read in all lines
print [line for line in open('some_file.txt', 'r')]

# We can apply functions to each item too
print [line.strip() for line in open('some_file.txt', 'r')]

# Also can use conditional statements
print [line.strip() for line in open('some_file.txt', 'r') if not 'another' in line]

# Also can do nested list comprehension! 
print [line.strip() for f in ['some_file.txt', 'some_other_file.txt'] for line in open(f, 'r')]