Python NameError exception not working as intended

Question

When I run this code, a NameError traceback error pops up, even though it should be handled by the exception. Why is that? The function call argument is intentionally misspelled.

filename_cats = "cats.txt"
filename_dogs = "dogs.txt"

def readlines(filename):
    """read lines from a text file"""
    try:
        with open(filename) as f:
            lines = f.readlines()
        string = ''
        for line in lines:
            string += line
    except (NameError, FileNotFoundError):
        print(f"The file {filename} was not found.")
    else:
        print(string)

readlines(filename_cat)

Answer 1

It's because the error happens here:

              ?
readlines(filename_cat) ?
              ??

Not anywhere in here:

try:
    with open(filename) as f:
        lines = f.readlines()
    string = ''
    for line in lines:
        string += line
except (NameError, FileNotFoundError):

A try..except block can only catch errors happening literally within it, not anything happening before or after it.