import string
import inspect
# Informal tutorial on the generators. We will cover very briefly:
## 1) What are the generators (PEP 255).
## 2) What is yield (PEP268).
# Generator in Python is a fancy object that maintain its state between calls.
# In simple words generator knows what to return you next on a next function call.
# And it doesn't need to store it in memory.
# Think of it as a computation on-demand. Lazy, yeah.
# Generator uses iterator protocol.
# Thus it is common to say that every generator is an iterator.
# It just means we can get a next value from the generator via next() call.
# You get a generator by asking to return one from a function.
# Theoretically, you can compute something blah blah to
# infinity using generators, and have very little memory footprint.
# The 'yield' keywoard in a function will cause the function
# instead of a value return a generator-iterator object.
# Lets demonstrate!
# lets define a function that will return us a generator-iterator object
# when we call it
def english_alphabet_generator_function():
for char in string.ascii_lowercase:
yield char
print english_alphabet_generator_function
# <function alphabet_generator at 0x1004c7320>, it is still a function
# Lets call english_alphabet_generator to get the actual generator object
alphabet_generator = english_alphabet_generator_function()
# calling the generator function will return a generator-iterator object.
print type(alphabet_generator)
# <type 'generator'>, not a function anymore, we got generator object
# Now lets examine function locals - varibales defined in the function namespace
print alphabet_generator.gi_frame.f_locals
# {}, nothing yet
# Now we can use iterator protocol and get print a few characters by calling generator's next() method.
print alphabet_generator.next() # prints 'a'
print alphabet_generator.next() # prints 'b'
print alphabet_generator.next() # prints 'c'
print alphabet_generator.gi_frame.f_locals
# prints {'char': 'c'}
# lets exauhst our generator and see what will happen
# it will print characters from d to y and throw 'StopIteration' exception
empty = False
while not empty:
try:
print alphabet_generator.next()
except(StopIteration) as exp:
empty = True
# Another not very useful example:
def _my_gen():
for x in xrange(200, 400):
yield 1
gen = _my_gen()
print("Sum:")
print(sum(gen)) # will print 200! :-)
# Please, refer to
# https://jeffknupp.com/blog/2013/04/07/improve-your-python-yield-and-generators-explained/ for a in-deep explanation with
# very interesting examples. Thank you!