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random/empty characters while re-editing a json file

I apologize for the vague definition of my problem in the title, but I really can't figure out what sort of problem I'm dealing with. So, here it goes.
I have python file:
edit-json.py
import os, json
def add_rooms(data):
if(not os.path.exists('rooms.json')):
with open('rooms.json', 'w'): pass
with open('rooms.json', 'r+') as f:
d = f.read() # take existing data from file
f.truncate(0) # empty the json file
if(d == ''): rooms = [] # check if data is empty i.e the file was just created
else: rooms = json.loads(d)['rooms']
rooms.append({'name': data['roomname'], 'active': 1})
f.write(json.dumps({"rooms": rooms})) # write new data(rooms list) to the json file
add_rooms({'roomname': 'friends'})'
This python script basically creates a file rooms.json(if it doesn't exist), grabs the data(array) from the json file, empties the json file, then finally writes the new data into the file. All this is done in the function add_rooms(), which is then called at the end of the script, pretty simple stuff.
So, here's the problem, I run the file once, nothing weird happens, i.e the file is created and the data inside it is:
{"rooms": [{"name": "friends"}]}
But the weird stuff happens when the run the script again.
What I should see:
{"rooms": [{"name": "friends"}, {"name": "friends"}]}
What I see instead:
I apologize I had to post the image because for some reason I couldn't copy the text I got.
and I can't obviously run the script again(for the third time) because the json parser gives error due to those characters
I obtained this result in an online compiler. In my local windows system, I get extra whitespace instead of those extra symbols.
I can't figure out what causes it. Maybe I'm not doing file handling incorrectly? or is it due to the json module? or am I the only one getting this result?

When you truncate the file, the file pointer is still at the end of the file. Use f.seek(0) to move back to the start of the file:
import os, json
def add_rooms(data):
if(not os.path.exists('rooms.json')):
with open('rooms.json', 'w'): pass
with open('rooms.json', 'r+') as f:
d = f.read() # take existing data from file
f.truncate(0) # empty the json file
f.seek(0) # <<<<<<<<< add this line
if(d == ''): rooms = [] # check if data is empty i.e the file was just created
else: rooms = json.loads(d)['rooms']
rooms.append({'name': data['roomname'], 'active': 1})
f.write(json.dumps({"rooms": rooms})) # write new data(rooms list) to the json file
add_rooms({'roomname': 'friends'})

Printing a PDF with Python from variable, instead a file

I would like to print a PDF file with an external printer. However, since I'm about to open, create or transform multiple files in some loop, I would like to print the thing without the need of saving it as a PDF file in every iteration.
Simplified code looks like this:
import PyPDF2
import os
pdf_in = open('tubba.pdf', 'rb')
pdf_reader = PyPDF2.PdfFileReader(pdf_in)
pdf_writer = PyPDF2.PdfFileWriter()
page = pdf_reader.getPage(0)
page.rotateClockwise(90)
# Some other operations done on the page, such as scaling, cropping etc.
pdf_writer.addPage(page)
pdf_out = open('rotated.pdf', 'wb')
pdf_writer.write(pdf_out)
pdf_print = os.startfile('rotated.pdf', 'print')
pdf_out.close()
pdf_in.close()
Is there any way to print "page", or "pdf_writer"?
Best regards

You can just use variables.
Eg.
path = 'C\yourfile.pdf'
os.startfile(path) #just pass the variable here

Python read from a file, and only do work if a string isn't found

So I'm trying to make a reddit bot that will exec code from a submission. I have my own sub for controlling these clients.
while __name__ == '__main__':
string = open('config.txt').read()
for submission in subreddit.get_new(limit = 1):
if submission.url not in string:
f.write(submission.url + "\n")
f.close()
f = open('config.txt', "a")
string = open('config.txt').read()
So what this is suppose to do is read from the config file, then only do work if the submission url isn't in config.txt. However, it always sees the most recent post and does it's work. This is how F is opened.
if not os.path.exists('file'):
open('config.txt', 'w').close()
f = open('config.txt', "a")

First a critique of your existing code (in comments):
# the next two lines are not needed; open('config.txt', "a")
# will create the file if it doesn't exist.
if not os.path.exists('file'):
open('config.txt', 'w').close()
f = open('config.txt', "a")
# this is an unusual condition which will confuse readers
while __name__ == '__main__':
# the next line will open a file handle and never explicitly close it
# (it will probably get closed automatically when it goes out of scope,
# but it's not good form)
string = open('config.txt').read()
for submission in subreddit.get_new(limit = 1):
# the next line should check for a full-line match; as written, it
# will match "http://www.test.com" if "http://www.test.com/level2"
# is in config.txt
if submission.url not in string:
f.write(submission.url + "\n")
# the next two lines could be replaced with f.flush()
f.close()
f = open('config.txt', "a")
# this is a cumbersome way to keep your string synced with the file,
# and it never explicitly releases the new file handle
string = open('config.txt').read()
# If subreddit.get_new() doesn't return any results, this will act as
# a busy loop, repeatedly requesting new results as fast as possible.
# If that is undesirable, you might want to sleep here.
# file handle f should get closed after the loop
None of the problems pointed out above should keep your code from working (except maybe the imprecise matching). But simpler code may be easier to debug. Here's some code that does the same thing. Note: I assume there is no chance any other process is writing to config.txt at the same time. You could try this code (or your code) with pdb, line-by-line, to see whether it works as expected.
import time
import praw
r = praw.Reddit(...)
subreddit = r.get_subreddit(...)
if __name__ == '__main__':
# open config.txt for reading and writing without truncating.
# moves pointer to end of file; closes file at end of block
with open('config.txt', "a+") as f:
# move pointer to start of file
f.seek(0)
# make a list of existing lines; also move pointer to end of file
lines = set(f.read().splitlines())
while True:
got_one = False
for submission in subreddit.get_new(limit=1):
got_one = True
if submission.url not in lines:
lines.add(submission.url)
f.write(submission.url + "\n")
# write data to disk immediately
f.flush()
...
if not got_one:
# wait a little while before trying again
time.sleep(10)

Setting HTML source for QtWebKit to a string value vs. file.read(), encoding issue?

I have a script that reads a bunch of JavaScript files into a variable, and then places the contents of those files into placeholders in a Python template. This results in the value of the variable src (described below) being a valid HTML document including scripts.
# Open the source HTML file to get the paths to the JavaScript files
f = open(srcfile.html, 'rU')
src = f.read()
f.close()
js_scripts = re.findall('script\ssrc="(.*)"', src)
# Put all of the scripts in a variable
js = ''
for script in js_scripts:
f = open(script, 'rU')
js = js + f.read() + '\n'
f.close()
# Open/read the template
template = open('template.html)
templateSrc = Template(template.read())
# Substitute the scripts for the placeholder variable
src = str(templateSrc.safe_substitute(javascript_content=js))
# Write a Python file containing the string
with open('htmlSource.py', 'w') as f:
f.write('#-*- coding: utf-8 -*-\n\nhtmlSrc = """' + src + '"""')
If I try to open it up via PyQt5/QtWebKit in Python...
from htmlSource import htmlSrc
webWidget.setHtml(htmlSrc)
...it doesn't load the JS files in the web widget. I just end up with a blank page.
But if I get rid of everything else, and just write to file '"""src"""', when I open the file up in Chrome, it loads everything as expected. Likewise, it'll also load correctly in the web widget if I read from the file itself:
f = open('htmlSource.py', 'r')
htmlSrc = f.read()
webWidget.setHtml(htmlSrc)
In other words, when I run this script, it produces the Python output file with the variable; then I try to import that variable and pass it to webWidget.setHtml(); but the page doesn't render. But if I use open() and read it as a file, it does.
I suspect there's an encoding issue going on here. But I've tried several variations of encode and decode without any luck. The scripts are all UTF-8.
Any suggestions? Many thanks!

NameError: global name is not defined

Hello
My error is produced in generating a zip file. Can you inform what I should do?
main.py", line 2289, in get
buf=zipf.read(2048)
NameError: global name 'zipf' is not defined
The complete code is as follows:
def addFile(self,zipstream,url,fname):
# get the contents
result = urlfetch.fetch(url)
# store the contents in a stream
f=StringIO.StringIO(result.content)
length = result.headers['Content-Length']
f.seek(0)
# write the contents to the zip file
while True:
buff = f.read(int(length))
if buff=="":break
zipstream.writestr(fname,buff)
return zipstream
def get(self):
self.response.headers["Cache-Control"] = "public,max-age=%s" % 86400
start=datetime.datetime.now()-timedelta(days=20)
count = int(self.request.get('count')) if not self.request.get('count')=='' else 1000
from google.appengine.api import memcache
memcache_key = "ads"
data = memcache.get(memcache_key)
if data is None:
a= Ad.all().filter("modified >", start).filter("url IN", ['www.koolbusiness.com']).filter("published =", True).order("-modified").fetch(count)
memcache.set("ads", a)
else:
a = data
dispatch='templates/kml.html'
template_values = {'a': a , 'request':self.request,}
path = os.path.join(os.path.dirname(__file__), dispatch)
output = template.render(path, template_values)
self.response.headers['Content-Length'] = len(output)
zipstream=StringIO.StringIO()
file = zipfile.ZipFile(zipstream,"w")
url = 'http://www.koolbusiness.com/list.kml'
# repeat this for every URL that should be added to the zipfile
file =self.addFile(file,url,"list.kml")
# we have finished with the zip so package it up and write the directory
file.close()
zipstream.seek(0)
# create and return the output stream
self.response.headers['Content-Type'] ='application/zip'
self.response.headers['Content-Disposition'] = 'attachment; filename="list.kmz"'
while True:
buf=zipf.read(2048)
if buf=="": break
self.response.out.write(buf)

That is probably zipstream and not zipf. So replace that with zipstream and it might work.

i don't see where you declare zipf?
zipfile? Senthil Kumaran is probably right with zipstream since you seek(0) on zipstream before the while loop to read chunks of the mystery variable.
edit:
Almost certainly the variable is zipstream.
zipfile docs:
class zipfile.ZipFile(file[, mode[, compression[, allowZip64]]])
Open a ZIP file, where file can be either a path to a file (a string) or
a file-like object. The mode parameter
should be 'r' to read an existing
file, 'w' to truncate and write a new
file, or 'a' to append to an existing
file. If mode is 'a' and file refers
to an existing ZIP file, then
additional files are added to it. If
file does not refer to a ZIP file,
then a new ZIP archive is appended to
the file. This is meant for adding a
ZIP archive to another file (such as
python.exe).
your code:
zipsteam=StringIO.StringIO()
create a file-like object using StringIO which is essentially a "memory file" read more in docs
file = zipfile.ZipFile(zipstream,w)
opens the zipfile with the zipstream file-like object in 'w' mode
url = 'http://www.koolbusiness.com/list.kml'
# repeat this for every URL that should be added to the zipfile
file =self.addFile(file,url,"list.kml")
# we have finished with the zip so package it up and write the directory
file.close()
uses the addFile method to retrieve and write the retrieved data to the file-like object and returns it. The variables are slightly confusing because you pass a zipfile to the addFile method which aliases as zipstream (confusing because we are using zipstream as a StringIO file-like object). Anyways, the zipfile is returned, and closed to make sure everything is "written".
It was written to our "memory file", which we now seek to index 0
zipstream.seek(0)
and after doing some header stuff, we finally reach the while loop that will read our "memory-file" in chunks
while True:
buf=zipstream.read(2048)
if buf=="": break
self.response.out.write(buf)

You need to declare:
global zipf
right after your
def get(self):
line. you are modifying a global variable, and this is the only way python knows what you are doing.