pdecrypt(Python:Simple Caesar Cipher)

Ever felt the need to encrypt text data. Now do it easily using pdencrypt(works on simple caesar cipher).This is a python program. After creating a file you would like to keep the python with you so that no one gets clue.Can be considered public domain work.You responsible for using the software properly You take liability of storing your own data and protecting it Programmer is not responsible for mistakes on part of user. If you have any suggestions feel free to coment.
Sorry small update for typo erors:
import string
name=raw_input('Enter file name: ')
def entangle(t):
    key=13
    lock=string.printable
    ret=''
    for wor in t:
        po=lock.find(wor)
        if po+key>=len(lock):
            po=((po+key)-(len(lock)-1))-1
        else:
            po+=key
        ret+=lock[po]
    return ret
def disentangle(t):
    key=13
    lock=string.printable
    ret=''
    for wor in t:
        po=lock.find(wor)
        if po-key<0:
            po=len(lock)+(po-key)
        else:
            po-=key
        ret+=lock[po]
    return ret

def read(name):
    file1=open(name,'r+')
    op=file1.readlines()
    for obj in op:
        obj=disentangle(obj)
        print obj
    file1.close()
def write(name):
    file1=open(name,'r+')
    t=raw_input('Enter ;')
    t=entangle(t)
    prev=file1.read()
    wr=prev+t+'\n'
    file1.close()
    file1=open(name,'w+')
    file1.write(wr)
    file1.close()
def main(name):
    file1=open(name,'r+')
    keyi=file1.readline()
    file1.close()
    key=raw_input('Enter your key: ')
    if key==disentangle(keyi[:-1]):
        while True:
            choi=raw_input('choice:')
            if choi=='1':
                read(name)
            elif choi=='2':
                write(name)
            elif choi=='3':
                break
            else:
                print 'invalid input'
                print 'program quitting'
                file1=open(name,'r+')
                prev=file1.read()
                wr=prev+'\n'
                file1.close()
                file1=open(entangle(name)+'.tri','w+')
                file1.write(wr)
                file1.close()
                file1=open(name,'w+')
                file1.write(name)
                file1.close()
    else:
        print 'Warning!! do not interfere encrypted txt'
        file1=open(name,'r+')
        prev=file1.read()
        wr=prev+'\n'+entangle('Warning!Someone tried to access your file')+'\n'
        file1.close()
def run():
    import os
    if os.path.isfile(name):
        main(name)
    else:
        file1=open(name,'w+')
        print 'This is important!!'
        print 'Your key is being set.'
        print 'You must remember this else your information stored is doomed'
        import random
        k=random.randint(10,len(string.printable)-1)
        print 'Your key is ',k
        stor=entangle(str(k))+'\n'
        file1.write(stor)
        file1.close()
        main(name)
run()