# Suppose you have a list of people's first names. You want to reduce the list down to only those people whose first names start with "C".

people = ['Amy', 'Alice', 'Bobby', 'Charlie', 'Connie', 'David']

# You would create a callback function that would look something like this:

def starts_with_c(name):
  if name[0] == "C":
    return True
  return False

# So then, you would run the filter function

starts_with_c_list = filter(starts_with_c, people)
print starts_with_c_list

# prints ['Charlie', 'Connie']

Shows usage of the Python filter() function

Python filter() function usage

data, filter

Python