Question about the groupby function

[new_to_python]

Hi, I have the following code:

import itertools
first_letter = lambda x: x[0]
names = ['Alan', 'Adam', 'Wes', 'Will', 'Albert', 'Steven']

for letter, names in itertools.groupby(names, first_letter):
   print(letter, list(names))

The program returned:

A ['Alan', 'Adam']
W ['Wes', 'Will']
A ['Albert']
S ['Steven']

Anybody knows why it does not return the result like the following?

A ['Alan', 'Adam', 'Albert']
W ['Wes', 'Will']
S ['Steven']