2016-02-26 Don't mix return and yield
When a function uses the keyword yield, it becomes a generator. A second function can accept this generator and produce another one as follows.
def generator(seq):
for v in range(0,3):
yield v+1
def generator2(gen):
for r in gen:
yield r
for v in generator2(generator(3)):
print(v)
[1]
1 2 3
This is not the only way to write this function. Python 3.5 has introduction keyword yield from.
def generator(seq):
for v in range(0,3):
yield v+1
def generator2(gen):
yield from gen
for v in generator2(generator(3)):
print(v)
[2]
1 2 3
The use of keyword return would give the same result in that case.
def generator(seq):
for v in range(0,3):
yield v+1
def generator2(gen):
return gen
for v in generator2(generator(3), False):
print(v)
[3]
1 2 3
However, it is not recommended to use if you use both return and yield in the same function. The second one works:
def generator(seq):
for v in range(0,3):
yield v+1
def generator2(gen, b):
if b :
return gen
else:
for r in gen:
yield r+1
for v in generator2(generator(3), False):
print(v)
[4]
2 3 4
But the first one does not work anymore.
def generator(seq):
for v in range(0,3):
yield v+1
def generator2(gen, b):
if b :
return gen
else:
for r in gen:
yield r+1
for v in generator2(generator(3), True):
print(v)
[5]
You need to use yield from:
def generator(seq):
for v in range(0,3):
yield v+1
def generator2(gen, b):
if b :
yield from gen
else:
for r in gen:
yield r+1
for v in generator2(generator(3), True):
print(v)
[6]
1 2 3
| <-- --> |
Xavier Dupré
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