Write a swap function without if-else.

The most Pythonic and recommended way to swap two variables a and b without an if-else statement is using tuple packing and unpacking: a, b = b, a.

This method works by first evaluating the right-hand side (b, a), which creates a temporary tuple containing the current values of b and a. Then, this tuple is unpacked, assigning its first element to a and its second element to b. This process is atomic and highly efficient in CPython, making it the preferred approach for its clarity and conciseness.

x, y = 10, 20
print(f"Before swap: x={x}, y={y}") # Output: Before swap: x=10, y=20
x, y = y, x
print(f"After swap: x={x}, y={y}")  # Output: After swap: x=20, y=10

Other methods exist, though generally less idiomatic in Python:

* XOR Swap: For integers, a^=b; b^=a; a^=b swaps values using bitwise XOR operations. This method avoids a temporary variable, historically useful in low-level languages, but is less readable and restricted to numeric types.
* Arithmetic Swap: a=a+b; b=a-b; a=a-b uses addition and subtraction. While it works for numbers, it carries a risk of integer overflow in languages with fixed-size integers (e.g., C, Java), though less of a concern in Python's arbitrary-precision integers. It also doesn't work for non-numeric types.
Conditional Swap (expression): While not strictly an "in-place" swap of a and b without any conditional logic, the expression (a, b) if condition else (b, a) returns a new tuple based on a condition, which can then be unpacked. This uses an if-else expression*, not a statement, to determine the order of assignment.

In the interview, also mention the importance of readability and Pythonic conventions. While these methods are clever, a, b = b, a is almost always the best choice due to its clarity and efficiency, aligning with principles of maintainable code, especially when working with data structures in frameworks like Pandas or Spark where new objects are often returned rather than modified in-place.