7. Generators¶

Lazy evaluation,
Memory effective

import collections, types

print(issubclass(types.GeneratorType, collections.Iterator))

True

Note

Generator is Iteratorem, but Iterator is not Generator !

7.1. Expression as generator¶

g = (n for n in range(20) if not n % 2) # just even !

for x in g:
    print(x)

7.2. Function as generator¶

def simple_gen():
    yield 5
    yield 10
    yield 15

s = simple_gen()

print(next(s))
print(next(s))
print(next(s))

5
10
15

# There are no elements to iterate over
print(next(s))

StopIteration:

def new_range(start=0, stop=None, step=1):
    i = start

    if stop is None:
        while True:
            yield i
            i += step
    else:
        while i < stop:
            yield i
            i += step

g = new_range(2, 5)

print(next(g))
print(next(g))

2
3

Note

Generators are functions generating next values. When iterator then we should have next() method.

7.3. Exercises part 1¶

Create generator, which is generating values which are 3 times greater than values from 0 to 20 ex. 0, 3, 6, 9, 12 …

7.4. Exercises part 2¶

Use file from list comprehension exercise list comprehension

Get this file using python

Hint

You can use library: urllib
You can use default function open and readline

Clean up the file,
Write generator converting date in text to date format,
Unfortunately, during logs creation we had our time set up badly. We need add 1 hour to the log hour

Hint

In package datetime there is timedelta