One of the less intuitive assignments to variables is augmented assignment to a list. The code here replaces a list variable by concatenation in several ways.
| M = "one two three".split() |
| M += ["four"] |
| M = "one two three".split() |
| M += [True] + M |
| M = "one two three".split() |
| M += "four" |
Most beginners do not see what is most
probably a bug in the last line of the example.
Realize that for a list M, an expression
M + 7 is an error because
concatenation only works if both terms are
sequences (7 is not a sequence). Technically,
M + "four" works because
"four" is a sequence (a string). That
explains how Python handles the last
augmented assignment of the example.