def freq(infile: TextIO, outfile: TextIO) -> None:
"""
given a file containing one digit per line, writes to a file,
a column where numbers are the frequency of the digits
"""
for line in infile:
count = 0
count += infile.count(int(line))
outfile.write(line + str(count))
def num_a(file: TextIO) -> int:
count = 0
for line in file:
count += file.count('a')
return count