UnboundLocalError: local variable referenced before assignment

[Chris Rebert]

On Tue, Jun 8, 2010 at 2:00 AM, ch1zra <ch1zra at gmail.com> wrote:
> On Jun 8, 10:29 am, Richard Thomas <chards... at gmail.com> wrote:
>> On Jun 8, 9:03 am, ch1zra <ch1... at gmail.com> wrote:
>> > I have following code :
>>
>> > import os, time, re, pyodbc, Image, sys
>> > from datetime import datetime, date, time
>> > from reportlab.lib.pagesizes import A4
>> > from reportlab.lib.units import cm
>> > from reportlab.pdfgen import canvas
>> > from reportlab.pdfbase import pdfmetrics
>> > from reportlab.pdfbase.ttfonts import TTFont
>> > import mkTable
>>
>> > mkTable.mkTable()
>>
>> > and then file mkTable.py located in same directory has :
>>
>> > def mkTable():
>> >     global canvas
>> >     canvas = canvas.Canvas(fname, pagesize=A4)
>> >     ... and so on
>>
>> > this gives me following traceback:
>>
>> > Traceback (most recent call last):
>> >   File "C:\py\pdf_test.py", line 36, in <module>
>> >     mkTable.mkTable()
>> >   File "C:\py\mkTable.py", line 38, in mkTable
>> >     canvas = canvas.Canvas("K_lista.pdf", pagesize=A4)
>> > UnboundLocalError: local variable 'canvas' referenced before
>> > assignment
>>
>> > i haven't posted entire code, because those lines are giving me
>> > problems. I've searched the web, and all say that I should make var
>> > global inside function. so I did it, but still nothing...
>> > using python 2.6.2 and reportlab 2.4
>> > help plz :)
>>
>> The version of mkTable.py you posted is clearly different to the one
>> in the traceback. You might want to check that.
>>
>> Richard.
>
> here's full version of mkTable.py (I've cut out all the drawing code
> for clarity)
> http://bpaste.net/show/7003/
>
> and it's caller :
> http://bpaste.net/show/7004/
>
> and the newest traceback (just generated):
>
> Traceback (most recent call last):
>  File "C:\py\pdf_test.py", line 36, in <module>
>    mkTable.mkTable()
>  File "C:\py\mkTable.py", line 38, in mkTable
>    canvas.setFillColorRGB(0.8,0.8,0.8)
> UnboundLocalError: local variable 'canvas' referenced before assignment

mkTable.py:
# -*- coding: utf-8 -*-
def mkTable():
    global canvas
<snip>
    canvas = canvas.Canvas("K_lista.pdf", pagesize=A4)

The only global variable defined in mkTable.py is the "mkTable"
function (partly since you don't import anything). So the reference to
the global variable "canvas" on the right-hand side of this expression
is completely undefined, resulting in the error you're getting.

In this respect, your code is akin to:
whatever.py:
# -*- coding: utf-8 -*-
def foo():
    global x
    x = 2 * x
foo()
# This is obviously horribly flawed since x is never given an initial value!
#EOF

More generally, your code uses "canvas" to refer both to the module
reportlab.pdfgen.canvas and an instance of the class
reportlab.pdfgen.canvas.Canvas; this is confusing and problematic. I
suggest you either rename one of them to something distinct (e.g.
`import reportlab.pdfgen.canvas as pdfcanvas`), or import just the
class Canvas straight from reportlab.pdfgen.canvas (i.e. `from
reportlab.pdfgen.canvas import Canvas`).

Cheers,
Chris
--
http://blog.rebertia.com