#! python3
# renameDates.py - Renames filenames with American MM-DD-YYYY date format
# to European DD-MM-YYYY.

import shutil, os, re

# Create a regex that matches files with the American date format.
datePattern = re.compile(r"""
        ^(.*?)          # all text before the date
        ((0|1)?\d)-     # one or two digits for the month
        ((0|1|2|3)?\d)- # one or two digits for the day
        ((19|20)\d\d)   # four digits for the year
        (.*?)$          # all the text after the date
        """, re.VERBOSE)

# Loop over the files in the working directory.
for amerFilename in os.listdir('.'):
    mo = datePattern.search(amerFilename)

    # Skip files without a date.
    if mo == None:
        continue

    # Get the different parts of the filename.
    beforePart = mo.group(1)
    monthPart = mo.group(2)
    dayPart = mo.group(4)
    yearPart = mo.group(6)
    afterPart = mo.group(8)

    # Form the European-style filename.
    euroFilename = beforePart + dayPart + '-' + monthPart + '-' + yearPart + afterPart

    # Get the full, absolute file paths.
    absWorkingDir = os.path.abspath('.')
    amerFilename = os.path.join(absWorkingDir, amerFilename)
    euroFilename = os.path.join(absWorkingDir, euroFilename)

    # Rename the files.
    print('Renaming "%s" to "%s"...' % (amerFilename, euroFilename))  # DEBUG
    #shutil.move(amerFilename, euroFilename)  # uncomment after testing

#! python3
# renameDates.py - Renames filenames with American MM-DD-YYYY date format
# to European DD-MM-YYYY.

import shutil, os, re

# Create a regex that matches files with the American date format.
datePattern = re.compile(r"""
        ^(.*?)          # all text before the date
        ((0|1)?\d)-     # one or two digits for the month
        ((0|1|2|3)?\d)- # one or two digits for the day
        ((19|20)\d\d)   # four digits for the year
        (.*?)$          # all the text after the date
        """, re.VERBOSE)

# Loop over the files in the working directory.
for amerFilename in os.listdir('.'):
    mo = datePattern.search(amerFilename)

    # Skip files without a date.
    if mo is None:
        continue

    # Get the different parts of the filename.
    beforePart = mo.group(1)
    monthPart = mo.group(2)
    dayPart = mo.group(4)
    yearPart = mo.group(6)
    afterPart = mo.group(8)

    # Form the European-style filename.
    euroFilename = beforePart + dayPart + '-' + monthPart + '-' + yearPart + afterPart

    # Get the full, absolute file paths.
    absWorkingDir = os.path.abspath('.')
    amerFilename = os.path.join(absWorkingDir, amerFilename)
    euroFilename = os.path.join(absWorkingDir, euroFilename)

    # Rename the files.
    print('Renaming "%s" to "%s"...' % (amerFilename, euroFilename))  # DEBUG
    #shutil.move(amerFilename, euroFilename)  # uncomment after testing

Update P04_renameDates: fixed equality operator with None