Python program to iterate through filenames and print sum of all currency detected

expenseSum.py

#   As a freelancer, I saved many receipts a day onto a cloud folder with a loose naming system
#   consisting of generally dollar amount + dates or some description of the expense.
#   As each folder has a slightly different system, here's a program where I could choose which
#   naming system I'm using in each folder before it spits out the sum of amount.

import re, os, decimal

#because float() is an approximation and gives weird decimal points
from decimal import Decimal

# file path for the folder which this program will iterate through filenames
path = input('paste path here: ')

os.chdir(path)

totalSum = 0
counter = 0

def resetNumber():
#   need to declare global, or will get UnboundLocalError
    global totalSum, counter
    totalSum = 0
    counter = 0

def expenseRun(regexToUse):
#   passing global variables to function
    global totalSum, counter
    resetNumber()
    if regexToUse == 'apple':
        appleExpense(totalSum, counter)
    elif regexToUse == 'banana':
        bananaExpense(totalSum, counter)
    elif regexToUse == 'cow':
        cowExpense(totalSum, counter)
    else:
        print('error! try again!')


def appleExpense(totalSum, counter):
    for filename in os.listdir():
        if apple.search(filename) == None:
            print('error! file name is '+filename)
        else:
            result = apple.search(filename)
            totalSum += Decimal(result.group(1))
            counter += 1
            print('receipt #' + str(counter) + '- ' +str(result.group(1))+' from '+str(result.group(2))+'. Now totaling at '+ str(totalSum) )
    print('\nTOTAL SUM IS: '+str(totalSum))

def bananaExpense(totalSum, counter):
    for filename in os.listdir():
        if banana.search(filename) == None:
            print('error! file name is '+filename)
        else:
            result = banana.search(filename)
            totalSum += Decimal(result.group(2))
            counter += 1
            print('receipt #' + str(counter) + '- ' +str(result.group(2))+' from '+str(result.group(1))+'. Now totaling at '+ str(totalSum) )
    print('\nTOTAL SUM IS: '+str(totalSum))

def cowExpense(totalSum, counter):
    for filename in os.listdir():
        if cow.search(filename) == None:
            print('error! file name is '+filename)
        else:
            result = cow.search(filename)
            totalSum += Decimal(result.group(1))
            counter += 1
            print('receipt #' + str(counter) + '- ' +str(result.group(1))+'. Now totaling at '+ str(totalSum) )
    print('\nTOTAL SUM IS: '+str(totalSum))

#re.compile(r'expression')

# group1 = another number of digits separated by a period (ex. "12.34")
# group2 = anything that comes after the digits and a space, and before ".pdf" file extension
apple = re.compile(r'(\d+\.\d+)\s+(.*)(\.pdf$)')

# group1 = any number of text + space + possible number (ex. "Mar 15")
# group2 = another number of digits separated by a period(ex. "12.34")
banana = re.compile(r'(.*)\s+(\d+\.\d+)')

# group1 = any number of text + space + possible number (ex. "Mar 15")
cow = re.compile(r'(\d+\.\d+)')

print('\nREGEX EXPRESSIONS! type out the one that applies---')
print('apple = $ first')
print('banana = $ later')
print('cow = $ only')

regexToUse = input('\nwhich regex? ')

expenseRun(regexToUse)

input("\nPress enter to exit;")