How can is solve "Name file is not defined"

When i run my Python command I keep seeing this error:

Traceback (most recent call last):
  file "<stdin>", line 1, in <module>
NameError: name 'file' is not defined

Can someone send my a copy from the following code but then good with a explain.

file = raw_input("Enter the file name: ")
file = open(file, "r")

Thanks!