How can I loop through blocks of lines in a file?

I have a text file that looks like this, with blocks of lines separated by blank lines:

ID: 1
Name: X
FamilyN: Y
Age: 20

ID: 2
Name: H
FamilyN: F
Age: 23

ID: 3
Name: S
FamilyN: Y
Age: 13

ID: 4
Name: M
FamilyN: Z
Age: 25

How can I loop through the blocks and process the data in each block? eventually I want to gather the name, family name and age values into three columns, like so:

Y X 20
F H 23
Y S 13
Z M 25

Answer

Here’s another way, using itertools.groupby. The function groupy iterates through lines of the file and calls isa_group_separator(line) for each line. isa_group_separator returns either True or False (called the key), and itertools.groupby then groups all the consecutive lines that yielded the same True or False result.

This is a very convenient way to collect lines into groups.

import itertools

def isa_group_separator(line):
    return line=='n'

with open('data_file') as f:
    for key,group in itertools.groupby(f,isa_group_separator):
        # print(key,list(group))  # uncomment to see what itertools.groupby does.
        if not key:               # however, this will make the rest of the code not work
            data={}               # as it exhausts the `group` iterator
            for item in group:
                field,value=item.split(':')
                value=value.strip()
                data[field]=value
            print('{FamilyN} {Name} {Age}'.format(**data))

# Y X 20
# F H 23
# Y S 13
# Z M 25