[reportlab-users] Possible bug?

[Les]

  Hello,

I have found an error, and I created a minimal working example. The minimal
working example starts with the very first example from Platypus user guide:

from reportlab.platypus import SimpleDocTemplate, Paragraph, Spacer
from reportlab.lib.styles import getSampleStyleSheet
from reportlab.lib.pagesizes import A4
from reportlab.lib.units import inch

PAGE_HEIGHT = A4[1]
PAGE_WIDTH = A4[0]
styles = getSampleStyleSheet()

Title = "Hello world"
pageinfo = "platypus example"


def myFirstPage(canvas, doc):
    canvas.saveState()
    canvas.setFont('Times-Bold', 16)
    canvas.drawCentredString(PAGE_WIDTH / 2.0, PAGE_HEIGHT - 108, Title)
    canvas.setFont('Times-Roman', 9)
    canvas.drawString(inch, 0.75 * inch, "First Page / %s" % pageinfo)
    canvas.restoreState()


def myLaterPages(canvas, doc):
    canvas.saveState()
    canvas.setFont('Times-Roman', 9)
    canvas.drawString(inch, 0.75 * inch, "Page %d %s" % (doc.page, pageinfo))
    canvas.restoreState()


def go():
    Story = [Spacer(1, 2 * inch)]
    style = styles["Normal"]
    for i in range(100):
        bogustext = ("This is Paragraph number %s. " % i) * 20
        p = Paragraph(bogustext, style)
        Story.append(p)
        Story.append(Spacer(1, 0.2 * inch))
    doc = SimpleDocTemplate("phello.pdf")
    doc.build(Story, onFirstPage=myFirstPage, onLaterPages=myLaterPages)


go()


If I change it to this (e.g. generate two identical files):

doc = SimpleDocTemplate("phello.pdf")
doc.build(Story, onFirstPage=myFirstPage, onLaterPages=myLaterPages)
doc = SimpleDocTemplate("phello2.pdf")
doc.build(Story, onFirstPage=myFirstPage, onLaterPages=myLaterPages)


then it builds phello.pdf correctly, but builds a totally empty phello2.pdf
(960 bytes, a single white empty page).

It is hard to explain as it is, but something even more interesting happens
if you try to make them totally independent, and create a copy of the story
as well:

import copy
doc = SimpleDocTemplate("phello.pdf")
doc.build(copy.copy(Story), onFirstPage=myFirstPage, onLaterPages=myLaterPages)
doc = SimpleDocTemplate("phello2.pdf")
doc.build(copy.copy(Story), onFirstPage=myFirstPage, onLaterPages=myLaterPages)


This will render phello.pdf correctly, and it will throw this error when
rendering phello2.pdf:

Traceback (most recent call last):
  File "C:\Projects\test\test2.py", line 48, in <module>
    go()
  File "C:\Projects\test\test2.py", line 45, in go
    doc.build(copy.copy(Story), onFirstPage=myFirstPage,
onLaterPages=myLaterPages)
  File
"C:\Users\nagyl\.virtualenvs\test-NC9-O-tN\lib\site-packages\reportlab\platypus\doctemplate.py",
line 1314, in build
    BaseDocTemplate.build(self,flowables, canvasmaker=canvasmaker)
  File "C:\Users\nagyl\.virtualenvs\
test-NC9-O-tN\lib\site-packages\reportlab\platypus\doctemplate.py", line
1079, in build
    self.handle_flowable(flowables)
  File "C:\Users\nagyl\.virtualenvs\
test-NC9-O-tN\lib\site-packages\reportlab\platypus\doctemplate.py", line
958, in handle_flowable
    raise LayoutError(ident)
reportlab.platypus.doctemplate.LayoutError: Flowable <Paragraph at
0x148e102cb80 frame=normal>This is Paragraph number 6. This is Paragraph
number 6. This(439.27559055118115 x 72) too large on page 1 in frame
'normal'(439.27559055118115 x 685.8897637795277) of template 'First'

And finally, here is the "solution" that solves all problems:


def go():
    def create_story():
        Story = [Spacer(1, 2 * inch)]
        style = styles["Normal"]
        for i in range(100):
            bogustext = ("This is Paragraph number %s. " % i) * 20
            p = Paragraph(bogustext, style)
            Story.append(p)
            Story.append(Spacer(1, 0.2 * inch))
        return Story

    doc = SimpleDocTemplate("phello.pdf")
    doc.build(create_story(), onFirstPage=myFirstPage,
onLaterPages=myLaterPages)
    doc = SimpleDocTemplate("phello2.pdf")
    doc.build(create_story(), onFirstPage=myFirstPage,
onLaterPages=myLaterPages)


This does not throw an error, and it renders both files correctly. It also
works if I do copy.deepcopy instead of copy.copy

I was looking for an explanation in the user guide. I was looking for a
note, telling me that a story can be used for document generation only
once. But there is no such thing in the docs. Or maybe I just did not find
it. Can somebody please explain what is happening here?

Environment details: Python 3.10.1 amd64 on Windows, reportlab 3.6.6

Note: it was also discussed here
https://mail.python.org/pipermail/python-list/2022-March/905724.html due to
a temporary problem with mailing list subscription.

Thanks,

    Laszlo
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