[FIXED] python: lambda, yield-statement/expression and loops (Clarify)

Issue

Can we implement yield or generator statement (with a loop) within a lambda?

My question is to clarify:

Whether the following simple loop function can be implemented with yield

def loopyield():
   for x in range(0,15):
      yield x
print(*loopyield())

Results in error:

lamyield=lambda x: yield x for x in range(0,15)
                       ^
SyntaxError: invalid syntax

Which looks like, it was expecting something as right operand for unwritten return statement but found the yield and getting confused.

Is there a proper legit way to achieve this in a loop?

Side note: yield can be statement/expression depending on who you ask: yield - statement or expression?

Final Answer : yield can be used with lambda but the limitation(single-line) makes it useless. for/while not possible in lambda because they are not expressions. -user2357112 implicit for loop is possible with list comprehension, and yield is valid within the list comprehension. -wim

Verdict- Explicit loops not possible because lambdas in python can only contain expressions, and to write an explicit loop you will need to use statements. -wim

Solution

The one-liner you seem to be trying to create is actually technically possible with a lambda, you just need to help the parser a bit more:

>>> lamyield = lambda: [(yield x) for x in range(15)]
>>> print(*lamyield())
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

This uses a for loop implicitly in a list comprehension. It is not possible with an explicit while loop or for loop outside of a comprehension. That's because lambdas in Python can only contain expressions, and to write an explicit loop you will need to use statements.

Note: this syntax is deprecated in Python 3.7, and will raise SyntaxError in Python 3.8

Answered By - wim