The itertools.groupby() function is a convenient way to group adjacent duplicate items of an iterable.

For instance, we can group a long string as follows:

from itertools import groupby

for key, group in groupby('YAaANNGGG'):

print(key, list(group))

# Y ['Y']

# A ['A']

# a ['a']

# A ['A']

# N ['N', 'N']

# G ['G', 'G', 'G']

Furthermore, we can harness its second argument to tell the groupby() function how to determine whether two items are the same or not:

from itertools import groupby

for key, group in groupby('YAaANNGGG', lambda x: x.upper()):

print(key, list(group))

# Y ['Y']

# A ['A', 'a', 'A']

# N ['N', 'N']

# G ['G', 'G', 'G']