how to understand this function with recursive call

Question

def pretty(e, level=0):
    if len(e) > 0:
        e.text = '\n' + '\t' * (level + 1)
        for child in e:
            pretty(child, level + 1)
        child.tail = child.tail[:-1]
    e.tail = '\n' + '\t' * level

---

This Python function uses a recursive call in its 5th line. It has a for-loop in the function with a loop variable called child. But in its 6th line, it has a child variable too. Please help me understand where child was defined.

Answer 1

When the loop is finished, the last element of the iterable e has been assigned to child. Since the smallest enclosing scope is the body of the function (for loops do not create their own scopes in Python), child is still in scope in the 6th line.

Answer 2

The variable 'child' is a variable declared inline by the 'for'.

Have a look at this c# example:

     foreach (PuzzlePiece **piece** in myPuzzle.pieces)
     {
        piece.DoSomething();
        Console.WriteLine( piece.WhatNumberPieceAmI());
     }

The Foreach is creating a scoped variable that will exist within the Foreach scope { }.

You are looking at the equivalent thing in your Python code.

Good Luck!