webapp2 - read-only file system error

Question

I'm developing a Google App Engine app using Python (webapp2) & Jinja2 and I'm trying to create a PDF file using the reportlab library.

Example:

from reportlab.pdfgen import canvas

class pdf(webapp2.RequestHandler):
  def get(self):
    x = 50
    y = 750
    c = canvas.Canvas("file.pdf")
    c.drawString(x*5,y,"Output")
    c.line(x,y-10,x*11,y-10)
    c.save()

When I run the server I'm getting the following error:

raise IOError(errno.EROFS, 'Read-only file system', filename)
IOError: [Errno 30] Read-only file system: u'file.pdf'

Answer 1

I got it to work by using StringIO:

from reportlab.pdfgen import canvas

# Import String IO which is a
# module that reads and writes a string buffer
# cStringIO is a faster version of StringIO
from cStringIO import StringIO

class pdf(webapp2.RequestHandler):
  def get(self):
    pdfFile = StringIO()

    x = 50
    y = 750
    c = canvas.Canvas(pdfFile)
    c.drawString(x*5,y,"Output")
    c.line(x,y-10,x*11,y-10)
    c.save()

    self.response.headers['content-type'] = 'application/pdf'
    self.response.headers['Content-Disposition'] = 'attachment; filename=file.pdf'
    self.response.out.write(pdfFile.getvalue())