[Python-Dev] PEP 572: Assignment Expressions

[Christoph Groth]

Nick Coghlan wrote:

> I also think that if "=" and ":=" both target the same kind of scope,
> there isn't enough new expressiveness introduced by the latter to
> justify the syntactic complexity of adding it.

OK, but then how about introducing assignment expressions with the "="
operator but *requiring* extra parens (similar to how modern C compilers
warn about assignment expressions without parens), e.g.

while (obj = get()):
    process(obj)

The semantics of assignment expressions could be exactly what I proposed
for ":=", i.e. completely consistent with assignment statements.

Assignment statements could be either left as they are or could be
treated as expressions.  That second choice would have consequences for
interactive sessions:

>>> a = 3
3

----------------

The above would bring the benefits of assignment expressions in a
minimally invasive but safe way.  Moreover, it would not feel like
Pascal!  The only downside is that "=" stands out less than ":=" so that
the presence of side-effects would be somewhat less visible.

Christoph