Python itertools

# Itertools

# Iterate over data structures that can be stepped over using a for-loop.

# Such data structures are also known as iterables.

# Itertools are more readable, fast, memory-efficient

# provides various functions that work on iterators to produce complex iterators.

# Infinite iterators: count, cycle, repeat

# Finite iterators: chain, compress, dropwhile

import itertools

# 1) Count - Infinite iterator

# print the first four even numbers

result = itertools.count(start = 0, step = 2)

for number in result:

if number < 8:

print (number)

else:

break

# Output:

# 0

# 2

# 4

# 6

# 2) Cycle - Infinite iterator

result = itertools.cycle('test')

counter = 0

for each in result:

if counter > 10:

break

counter += 1

print(each)

# Output:

# t

# e

# s

# t

# t

# e

# s

# t

# t

# e

# s

# 3) Repeat - Infinite iterator

result = itertools.repeat('test', 2)

for each in result:

print(each)

# Output:

# test

# test

# 1) Chain - Finite iterator

l1 = ['aaa', 'bbb', 'ccc']

l2 = ['ddd', 'eee', 'fff']

result = itertools.chain(l1, l2)

for each in result:

print(each)

# Output:

# aaa

# bbb

# ccc

# ddd

# eee

# fff

# 2) Compress - Finite iterator

l1 = ['aaa', 'bbb', 'ccc']

l2 = [True, False, False]

result = itertools.compress(l1, l2)

for each in result:

print(each)

# Output:

# aaa

# 3) Dropwhile - Finite iterator

# keeps on dropping values from the iterable until it encounters the first element

def is_positive(n):

return n > 0

value_list =[5, 6, -8, -4, 2]

result = list(itertools.dropwhile(is_positive, value_list))

print(result)

# Output:

# [-8, -4, 2]

# 4) groupby

ll = [("aaa", 1), ("aaa", 2), ("bbb", 3), ("bbb", 4)]

# Key function

key_func = lambda y: y[0]

for key, group in itertools.groupby(ll, key_func):

print(key + " :", list(group))

# Output:

# aaa : [('aaa', 1), ('aaa', 2)]

# bbb : [('bbb', 3), ('bbb', 4)]