Python Generators (Page: 2)
Generator expressions in Python
Generator expressions are generator version for list comprehensions, but return generator instead of list.
a = (x*x for x in range(10)) # define generator of list of squares
print( a ) # at 0x7fc2a414cd00>
print( type(a) ) # It is important to understand, that this generator will only be executed when it will be used, and after its iterator will be pointed to the end of its generating values
a = (x*x for x in range(10)) # we define generator of ten squares here
l1=list(a) # call generator and store everything into a list
print( l1 ) # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
l2=list(a) # call again this generator, but it is already 'used'
print( l2 ) # []One more example of usage of this 10 squares generator
sq = (x*x for x in range(10)) # we define generator of ten squares here
print( sum(sq) ) # 285
print( sum(sq) ) # 0 - it is already 'used'List of pythogorian triplets with generators
Very simple task is to find N pythogorian triplets with generator. Pythogorian triplets and a triplets of integers (x,y,z) where
x*x + y*y == z*z; or x**2 + y**2 == z**2
Please go to Page 1 for definition of out generators integers() and take()
PTgen = ((x, y, z) for z in integers() for y in range(1, z) for x in range(1, y) if x*x + y*y == z*z)
tr = take(5, PTgen) # we will generate 20 triangles
print( tr ) # [(3, 4, 5), (6, 8, 10), (5, 12, 13), (9, 12, 15), (8, 15, 17)] You can use generator one by one with function next(). In this case generator will remenr it's iteration
sq = (x*x for x in integers()) # See previous page for integers() definition
print( next(sq) ) # 1
print( next(sq) ) # 4
print( next(sq) ) # 9
print( next(sq) ) # 16How to join generator into a string
It is possible to join generator into a string with function .join(). It is important to remember that this generator must produce object of STR type.
new_string = '-'.join(str(x) for x in range(10)) # 0-1-2-3-4-5-6-7-8-9
Published: 2021-09-25 11:31:46
Updated: 2021-10-12 10:39:24