import re

p = '(\d+)'
pgroups = '(\d+)-(\d+)-(\d+)'
p2 = '-\d{2}-'
ssn = '012-34-5678'

# Returns a list: [ '012', '34', '5678' ]
matches_list = re.findall(p, ssn)

# Returns an iterator
matches_it = re.finditer(p, ssn)
for m in matches_it:
  print('{0}-{1}: {2}'.format(m.start(), m.end(), m.group(0)))

# re.match matches only the beginning of a string if starting position is not specified
# re.search scans the whole string
# So this does not match:
match = re.match(p2, ssn)

# Which means this is None:
type(match)

# While this successfully returns a match object
match = re.search(p2, ssn)
type(match)
print('{0}-{1}: {2}'.format(match.start(), match.end(), match.group(0)))

# With multiple groups in a match object, .group(0) and .group() return the full set of matches
# While .group(n) returns the nth group
# And .groups() returns a tuple of the groups
ssnmatch = re.search(pgroups, ssn)
print('Match: {0}'.format(ssnmatch.group(0)))
print('Tuple: {0}'.format(ssnmatch.groups()))
for group in range(1, len(ssnmatch.groups()) + 1):
  print('Match group: {0}'.format(ssnmatch.group(group)))