#!/usr/bin/env python
# coding: utf-8

# ### Comprehensions are good, but not memory efficient. They may create	a	whole	new	list

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# Copyright 2014 Brett Slatkin, Pearson Education Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# Preamble to mimick book environment
import logging
from pprint import pprint
from sys import stdout as STDOUT


# ### Need to 	hold the	length	of	every	line	of	the file	in	memory. BAD!

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# Example 1
import random
with open('my_file.txt', 'w') as f:
    for _ in range(10):
        f.write('a' * random.randint(0, 100))
        f.write('\n')

value = [len(x) for x in open('my_file.txt')]
print(value)


# ### A	generator	expression () does not make forward progress. GOOD!

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# Example 2
it = (len(x) for x in open('my_file.txt'))
print(it)


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### It returns iterator.


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# Example 3
print(next(it))
print(next(it))


# ### generator	expressions	can	be	composed	together. Create a new generator using 'it'! WONDERFUL!!

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# Example 4
roots = ((x, x**0.5) for x in it)
print(roots)


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# Example 5
print(next(roots))