file_Name1 = 'abc123de'
file_Name2 = 'qwe987rty'

file_Name1 = 'abc123de'
# store that string as a list of characters
L1 = list(file_Name1)
# call filter on it using a lambda expression
L1 = filter(lambda x: x in '1234567890', L1)
# L1 now = ['1', '2', '3']
num_digits = len(L1)

filter(function, iterable)
 
    Construct a list from those elements of iterable for which function returns true. iterable may be either a sequence, a container which supports iteration, or an iterator. If iterable is a string or a tuple, the result also has that type; otherwise it is always a list. If function is None, the identity function is assumed, that is, all elements of iterable that are false are removed.
 
    Note that filter(function, iterable) is equivalent to [item for item in iterable if function(item)] if function is not None and [item for item in iterable if item] if function is None.
 
    See itertools.filterfalse() for the complementary function that returns elements of iterable for which function returns false.

#example using regular expressions
import re
 
# here's the string we'll be searching:
myStr = "abc123def"
 
# search through the string using a regular expression
# this regex will return any decimal digits (0-9) it finds in the string
temp = re.search('[0-9]+', myStr)
# you could also use the following regex:
# m = re.search('\d+', myStr)
# which is another way of writing the above expression
 
# now lets process the results of the search...
result = temp.group()
 
numDigits = len(result)
 
print "In the string:", myStr, "- There were", numDigits, "numerical digits found, the digits were", result

# regular expressions example 2
import re
 
myStr="abc123def"
 
print "Number of digits =", len( (re.search('[0-9]+', myStr)).group() )

import re
 
myStr="abc123def456"
 
result = re.findall('[0-9]+', myStr)
 
numDigits = 0
for i in result:
    numDigits+=len(i)
 
print "String:", myStr
print "Digits found:", result
print "Number of digits =", numDigits