How to loop through previous lines

[Atrisa]

Hi everyone. I have a text file looking like this:

Book ID: 1
Availability: on shelf > 3 borrows > 2
Name: Bread and Wine
Writer: Silone

Book ID: 2
Availability: on shelf > 4 borrows > 1
Name: Fontamara
Writer: Silone

Book ID: 3
Availability: on shelf > 3 borrows > 2
Name: Poirot
Writer: Agatha Christie

Book ID: 4
Availability: on shelf > 2 borrows > 2
Name: Miss Marple
Writer: Agatha Christie

and so on. I want to count the number of books by each writer and the total amount of their books been borrowed so far, to have a list like this:
-------------
Siolne 2 3
A. Christie 2 4
---------------

I have no idea how to go through this kind of blocks and specially grab a previous line from the block. Any help is appreciated.

[bvdet]

Initialize a dictionary dd = {}
Loop through each line of text
If the line starts with "Writer", split the line on the colon character, add the writer to the dictionary as a key with a quantity of one.
If the writer is already in the dictionary, increment the value by one
OR the writer could be added this way:

    v = dd.get('Agatha Christie', 0)
    dd['Agatha Christie'] = v+1

[Atrisa]

This is what I did, but don't know why it doesn't print anything:

f = open('test.txt').read()
 
dd = {}
for line in f.split('\n\n'):
    if line.startswith('Writer'):
        writer = line.split(':')[0]
        dd.get(writer, 0)
        dd[writer] += 1
print dd
 

[bvdet]

The way you did it, use dd.setdefault() instead of dd.get(). If you want the author's name, use index [1] instead of [0].

[Atrisa]

Still the dictionary is empty.

[Atrisa]

Now it is working.

dd = {}
for line in open('test.txt'):
    if line.startswith('Writer'):
        writer = line.split(':')[1].strip('\n')
        dd.setdefault(writer, 0)
        dd[writer] += 1
print dd
 

[bvdet]

Good job Atrisa!

BV

[Atrisa]

Thanks BV for your hints, helps and instructions:)