[EMAIL PROTECTED] wrote: > Ok, I'm relatively new to Python (coming from C, C++ and Java). I'm > working on a program that outputs text that may be arbitrarily long, > but should still line up, so I want to split the output on a specific > column boundary. Since I might want to change the length of a column, > I tried defining the column as a constant (what I would have made a > "#define" in C, or a "static final" in Java). I defined this at the > top level (not within a def), and I reference it inside a function. > Like this: > > COLUMNS = 80 > > def doSomethindAndOutputIt( ): > ... > for i in range( 0, ( len( output[0] ) / COLUMNS ) ): > print output[0][ i * COLUMNS : i * COLUMNS + ( COLUMNS - 1 ) ] > print output[1][ i * COLUMNS : i * COLUMNS + ( COLUMNS - 1 ) ] > .. > > etc. etc. It works fine, and splits the output on the 80-column > boundary just like I want. > > Well, I decided that I wanted "COLUMNS = 0" to be a special "don't > split anywhere" value, so I changed it to look like this: > > COLUMNS = 80 > > def doSomethindAndOutputIt( ): > ... > if COLUMNS == 0: > COLUMNS = len( output[ 0 ] ) > > for i in range( 0, ( len( output[0] ) / COLUMNS ) ): > print output[0][ i * COLUMNS : i * COLUMNS + ( COLUMNS - 1 ) ] > print output[1][ i * COLUMNS : i * COLUMNS + ( COLUMNS - 1 ) ] > .. > > Now, when I run it, I get the following error: > > Traceback (most recent call last): > File "Test.py", line 140, in ? > doSomethingAndOutput( input ) > File "Test.py", line 123, in doSomethingAndOutput > if COLUMNS == 0: > UnboundLocalError: local variable 'COLUMNS' referenced before > assignment > > I went back and re-read chapter 13 of "Learning Python", which talks > about variable scoping rules, and I can't figure out why Python is > saying this variable in Unbound. It works if I insert: > > global COLUMNS > > before the "if" statement... but I don't understand why. Is the > interpreter scanning my entire function definition before executing > it, recognizing that I *might* assign COLUMNS to a value, and deciding > that it's a local on that basis?
Yep. That's essentially it. Because python has no explicit variable declaration, it looks on the left hand side of assignments to determine the locals. Diez -- http://mail.python.org/mailman/listinfo/python-list
