Python - Function Generator functions
Introduction
The following code defines a generator function that can be used to generate the squares of a series of numbers:
def gensquares(N): for i in range(N): yield i ** 2 # Resume here later
This function yields a value by using yield statement.
When using yield statement, it returns value to its caller, each time through the loop and when it is resumed, its prior state is restored.
Demo
def gensquares(N): for i in range(N): yield i ** 2 # Resume here later # ww w . j ava2 s. com for i in gensquares(5): # Resume the function print(i, end=' : ') # Print last yielded value
Result
To end the generation, functions either use a return statement with no value or fall off the end of the function body.
To see what is going on inside the for, call the generator function directly:
Demo
def gensquares(N): for i in range(N): yield i ** 2 # Resume here later # from w w w . j a va2s .c o m x = gensquares(4) print( x )
Result
x is a generator object that supports the iteration protocol.
The returned generator object has a __next__ method that starts the function or resumes it from where it last yielded a value.
It raises a StopIteration exception when the end of the series of values is reached.
Demo
def gensquares(N): for i in range(N): yield i ** 2 # Resume here later # www. ja va2 s.c o m x = gensquares(4) print( x ) print( next(x) ) # Same as x.__next__() in 3.X print( next(x) ) # Use x.next() or next() in 2.X print( next(x) ) print( next(x) ) print( next(x) )
Result
generators return themselves for iter.
Demo
def gensquares(N): for i in range(N): yield i ** 2 # Resume here later # from www.j a v a 2s .c om y = gensquares(5) # Returns a generator which is its own iterator iter(y) is y # iter() is not required: a no-op here print( next(y) ) # Can run next()immediately
Result
