为什么我看到“ IndexError：字符串索引超出范围”

Question

I'm trying to use reportlab's pdfgen to draw a PDF, but when I try to save my canvas I get this big cranky error:

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
/usr/local/bin/ipython-listener in <module>()
----> 1 c = set_canvas(); c.save()

/usr/lib/python2.7/dist-packages/reportlab/pdfgen/canvas.pyc in save(self)
   1191            If there is current data a ShowPage is executed automatically.
   1192            After this operation the canvas must not be used further."""
-> 1193         if len(self._code): self.showPage()
   1194         self._doc.SaveToFile(self._filename, self)
   1195 

/usr/lib/python2.7/dist-packages/reportlab/pdfgen/canvas.pyc in showPage(self)
    582 
    583         pageWidth = self._pagesize[0]
--> 584         pageHeight = self._pagesize[1]
    585         cM = self._cropMarks
    586         code = self._code

IndexError: string index out of range

This is the relevant code:

from reportlab.pdfgen import canvas
from reportlab.lib.pagesizes import landscape, letter
from reportlab.lib.units import inch

def set_canvas():
    c = canvas.Canvas("bingo.pdf")
    c.setPageSize(letter)
    c.setPageRotation(90)
    c.setFont('Helvetica-Bold', 14)
    return c

And once that's loaded I run c = set_canvas() and c.save() and get the error. If I comment out the setPageSize line it seems to work:

def set_canvas():
    c = canvas.Canvas("bingo.pdf")
    c.setPageRotation(90)
    c.setFont('Helvetica-Bold', 14)
    return c

c = set_canvas()    
c.drawString(72, 72, "Why is this so hard?")
c.save()

But I only started having this problem when I added in the font size. I can't figure out what I'm missing here.

Answer 1

from reportlab.lib.pagesizes import landscape, letter sets letter as a tuple (612.0, 792.0) -- but I was using "letter" as a variable inside a function later in my script, effectively redefining it as a string. And a string has no index [1] so it was out of range when reportlab tried to set the pageHeight with pageHeight = self._pagesize[1]

Not for nothing, running pylint would have clued me in to the problem a lot faster.