What is Python's A, B = B, A?

A,B=B,A replaces the contents of the two variables A,B.It is called multiple assignments, and can be interpreted as doing B values in A and A values in B at the same time.Before and after this substitution, A, B content print is easy to understand.

In non-Python languages, it is common to have a third temporary variable ready to replace two variables (so-called swap operations):

tmp=B
B = A
A = tmp

Python allows you to write something similar in one line.

 A, B = B, A

More precisely, this substitution is achieved by unpacking the tuple and sequence.In other words, the right side is interpreted as a tuple (B,A), and then the unpacking operation is performed, resulting in multiple substitutions.

• References
  • 5.3. Tuples and Sequences -- Python 3 Documentation
  • Unpack tuples and lists in Python (expand and substitute multiple variables) --note.nkmk.me

• 5.3. Tuples and Sequences -- Python 3 Documentation
• Unpack tuples and lists in Python (expand and substitute multiple variables) --note.nkmk.me