Finding Hyperlinks in Python 3 - python-3.x

Question

So my assignment is to write a program that reads all data from a web page and prints all hyperlinks of the form:
link text
So far I've gotten this far with the help of my instructor.
from urllib.request import urlopen
def findTitle(webpage):
encoding = "utf-8"
for webpagestr in webpage:
webpagestr = str(webpagestr,encoding)
if "<title>" in webpagestr:
indexstart = webpagestr.find("<title>")
indexend = webpagestr.find("</title>")
title = webpagestr[indexstart+7:indexend]
return title
return title
def H1headings(webpage):
encoding = "utf-8"
for webpagestr in webpage:
webpagestr = str(webpagestr,encoding)
if "<h1>" in webpagestr:
indexstart = webpagestr.find("<h1>")
indexend = webpagestr.find("</h1>")
heading = webpagestr[indexstart+4:indexend]
print(heading)
def main():
address = input("Enter URL to find title and more information: ")
try:
webpage = urlopen(address)
title = findTitle(webpage)
print("Title is", title)
H1headings(webpage)
webpage.close()
except Exception as exceptObj:
print("Error: ", str(exceptObj))
main()
When I run this program it allows me to input a URL but after it gives me a:
Error: local variable 'title' referenced before assignment
I'm not sure what it means.
Then one of my attempts when I placed:
def findTitle(webpage):
title = "Not Found"
encoding = "utf-8"
ran the program, it would give me:
Enter URL to find title and more information: http://jeremycowart.com
Title is not found
Jeremy Cowart
It's what I'm looking for, but I believe I'm suppose to have the title and heading as well as link text.
I've gotten close but I just can't figure it out. Any help would be appreciated!

Answer 1

There are at least a couple problems I see.
In your function findTitle, you always return the variable title, even if you haven't found one, and therefore haven't set the variable title to anything, hence when it fails to find a title on the web page (whether because there isn't one or your code failed to find it) it's returning a variable that hasn't been created/assigned yet.
First, you should fix your code so it doesn't do that. You can either change the final return statement to return a default value, e.g. "Not found" or you can set title to the default value at the top of your function, which guarantees it will exist no matter when it is returned, e.g.:
def foo(x):
y = -1
<do stuff, maybe re-setting y>
return y
That is the pattern I tend to prefer.
There is another problem though, which is preventing you from properly detecting the title. If you step through your program you should see it. Essentially, you start looping, get the first line, check to see if it has a title; if it does you return it (good), if it doesn't you skip the if, but then you return it anyway (not so good) and you never get to the second line.