# 1. Import the module that provides support for regular expression
# 2. Define a regular expression
# 3. Mark regular expressions as raw strings  (r'...')
# 4. Create a regular expression object that matches the pattern
#    using re.compile(r'.....')
# 5. Use the regular expression object to search or find
#    certain patterns in the given string

# (let's call regular expression object as regex for short)


import re      # import module for regular expression

# define a regular expression, mark it as a raw string,
# then compile the raw string to create a regex object
number_finder = re.compile(r'([1-9])([0-9]*)')     # defined in 2 groups
# grouping is determined by (..)
# in this example, there are two groups:
#   group 1 is ([1-9])
#   group 2 is ([0-9]*)

print(number_finder)    # let's see what pattern looks like

# let's create some string,
# we'll later use the regex object to look for
# certain patterns in this string
text = 'one two 1234 four 56 78ninety 1111a'

# search() returns the first matched object
matched = number_finder.search(text)
print('first matched is', matched)

# start() returns the first index of the match
print('start() =', matched.start())

# end() returns the last index of the match
print('end() =', matched.end())

# group() returns the matched object
print('group() =', matched.group())

# groups() returns all matching subgroups in a tuple
# applicable only if the regular expression is defined in groups
print('groups() =', matched.groups())
print('number of groups in matched =', len(matched.groups()))
print('matched.group() =', matched.group(), '= matched.group(0) =', matched.group(0))
print('  matched.group(1) =', matched.group(1))   # return subgroup 1
print('  matched.group(2) =', matched.group(2))   # return subgroup 2


# print('  group() =', matched.group(), \
#       '  start() =', matched.start(), \
#       '  end() =', matched.end(),
#       '  groups() =', matched.groups())


print('matched from index', matched.start(), 'to', matched.end(), 'of text is', text[matched.start():matched.end()])

print('finditer(text) -->')
for m in number_finder.finditer(text):
    print(' ', m.group(), '--> subgroup =', m.group(1), ':', m.group(2))