CODEWITHSUNDEEP
pythonpython-3.xsyntax
DevFallingstar
DevFallingstar

Reputation: 74

What is difference between a=b=c and assign separately in programmatically?

Is there any difference between:

a=b=c

and 

b = c
a = c

in python?
Will the interpreter read those things differently?

And what is the side effect when i use first/second method, if it has side effects?

Upvotes: 0

Views: 59

Answers (2)

Ignacio Vazquez-Abrams
Ignacio Vazquez-Abrams

Reputation: 798686

If c is an existing object then both pieces of code will have the same effect, binding both a and b to the same existing object.

If c is a literal then the first will bind them to the same object whereas the second will create two separate objects (for a certain value of "create"; the difference only matters for mutable objects) and bind them to each name.

Upvotes: 1

mattjegan
mattjegan

Reputation: 2884

For your future googling, this is known as a "chained assignment" or "nested assignment". As shown by this answer chained assignments are useful for forcing the interpreter to only evaluate the right hand expression once. For example:

a = b = myComputeHeavyFunc()  # Only one evaluation

will only evaluate myComputeHeavyFunc() once where as the multi-line solution evaluates the function twice, providing a performance loss:

a = myComputeHeavyFunc()  # One evaluation
b = myComputeHeavyFunc()  # Another evaluation

Upvotes: 2

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