Assignment in conditional not permitted in Python?

Question

Why is code like

if a = "hello":
    pass

invalid in Python? The a = "Hello" is just a expression whose value is the Rvalue. It's valid in most languages like C or php. Some opinions?

If you tell your C compiler to emit warnings, it'd warn you while making an assignment in a condition. — devnull
– devnull, Commented Mar 24, 2014 at 3:30

Hugh Bothwell · Accepted Answer · 2014-03-24 03:38:41Z

2

While Python will allow you to chain assignment,

a = b = "hello"

it will not allow you to use it in an expression,

"hi" > b = "hello"    # => Syntax error

This is for safety, to keep you from accidentally using = when you meant ==

answered Mar 24, 2014 at 3:38

Hugh Bothwell

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1 Comment

Chenglu Over a year ago

thanks a lot. It really confused me when the a = b = "hello" is valid while the if a = "hello is invalid. But I don't think it is necessary for experienced developers.

user1342784 · Accepted Answer · 2014-03-24 03:40:58Z

1

This is intentionally made illegal in python as allowing it is a huge source of error and making it illegal is a minor inconvenience.

See the Design and History FAQ

My experience in python is that this is basically right. I rarely miss not being able to do this.

answered Mar 24, 2014 at 3:40

user1342784

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