Why is omitting parentheses around yield expression not allowed in function call?

Python Help
1

I’ve stumbled upon this while writing a custom auth scheme for HTTPX today. Parentheses can be omitted around a yield expression if on the right side of an assignment expression (as mentioned here, last paragraph), but not within a function call.

I did a quick read of PEP 255, and search this forum, but did not find a straight answer.

# Ok
def printgen():
    while True:
        x = yield
        print(x)

# Also ok
def printgen():
    while True:
        print((yield))

# SyntaxError
def printgen():
    while True:
        print(yield)

In contrast, await expressions can be used in function calls within coroutine functions.

# Ok
print((await asyncio.sleep(1)))

# Also ok
print(await asyncio.sleep(1))

I suspect this has something to do with await expressions requiring a right hand expression unlike yield expressions.
I’ll be glad if someone can give me a clear explainer!

2

The parentheses are definitely Python syntax. But as to why they were made part of the syntax, I couldn’t say.