"Sandro Dentella" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > I'd like to understand why += operator raises an error while .append() > does > not.
Your mistake is thinking of '+=' as an operator. In Python terms it is not, any more than '=' is. In Python, neither 'a=b' nor 'a+=b' is an expression. Both symbols are statement symbols that define assigment statements (augmented in the former case). "a.append(b)" is an expression with side effects used as a statement. > Traceback (most recent call last): > File "c1.py", line 26, in ? > x = foo() > File "c1.py", line 7, in __init__ > print "a: ", a > UnboundLocalError: local variable 'a' referenced before assignment This is the clue that you did not get. It tells you that the parser thinks 'a' is local, which means you rebound the name 'a' *somewhere* in the function, even if not as obviously as a simple assignment "a = whatever". It turns out that augmented assignment statements are assignments statements ;-). Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
