Pattern in a file

More general snippet on the same subject can be found at scan filetree for files containing text

a,b are are really bad variable names.
It`s ok to use only in small code examples,should not be used in finish scripts.
if b in i really easy to understand?
Bare except: should not be used.
I explain better why not in this post.
http://www.daniweb.com/software-development/python/threads/423971/python-program-detect-if-files-exist#post1812471
There is no need to use found 0 and 1.

So a more pythonic version would look like this.

def find():
    file_in = raw_input("Insert file: ")
    pattern = raw_input("Insert pattern: ")
    try:
        with open(file_in) as a_file:
            for file_content in a_file:
                if pattern in file_content:
                    return 'Pattern was found'
                return 'Pattern was not found'
    except IOError:
        return "Invalid file."

print find()

Ok, for me something like this would go (but preferably I would invoke fileselection dialog to choose file)

import os

def read_valid(case_insensitive=True):
    while True:
        try:
            file_in = raw_input("Give valid file name: ")
            with open(file_in) as infile:
                return infile.read().lower() if case_insensitive else infile.read()
        except IOError:
            print "Invalid file.\nFiles in current directory are:\n\t%s" % '\n\t'.join(os.listdir('.'))

def find(pattern, case_insensitive=True):
    if case_insensitive:
        pattern = pattern.lower()
    return 'Pattern was %sfound.' % ('' if pattern in read_valid(case_insensitive) else 'not ')


print find(raw_input("Pattern to find: "))

def find():
    file = raw_input("Insert file: ")
    pattern = raw_input("Insert pattern: ")
    try:
        if any(iter for iter in open(file, 'r') if pattern in iter): print "Patter was found."
        else: print "Pattern was not found."
    except:
        print "Invalid file."
find()

As pyTony suggested for an inline-searching.

iter is built in function, so use other variable name to avoid confusion.