如何在python中的匹配行之后抓取行

Question

I am an amateur using Python on and off for some time now. Sorry if this is a silly question, but I was wondering if anyone knew an easy way to grab a bunch of lines if the format in the input file is like this:

" Heading 1

Line 1

Line 2

Line 3

Heading 2

Line 1

Line 2

Line 3 "

I won't know how many lines are after each heading, but I want to grab them all. All I know is the name, or a regular expression pattern for the heading.

The only way I know to read a file is the "for line in file:" way, but I don't know how to grab the lines AFTER the line I'm currently on. Hope this makes sense, and thanks for the help!

*Thanks for all the responses! I have tried to implement some of the solutions, but my problem is that not all the headings are the same name, and I'm not sure how to work around it. I need a different regular expression for each... any suggestions? *

Answer 1

Generator Functions

def group_by_heading( some_source ):
    buffer= []
    for line in some_source:
        if line.startswith( "Heading" ):
            if buffer: yield buffer
            buffer= [ line ]
        else:
            buffer.append( line )
    yield buffer

with open( "some_file", "r" ) as source:
    for heading_and_lines in group_by_heading( source ):
        heading= heading_and_lines[0]
        lines= heading_and_lines[1:]
        # process away.

Answer 2

You could use a variable to mark where which heading you are currently tracking, and if it is set, grab every line until you find another heading:

data = {}
for line in file:
    line = line.strip()
    if not line: continue

    if line.startswith('Heading '):
        if line not in data: data[line] = []
        heading = line
        continue

    data[heading].append(line)

Here's a http://codepad.org snippet that shows how it works: http://codepad.org/KA8zGS9E

Edit : If you don't care about the actual heading values and just want a list at the end, you can use this:

data = []
for line in file:
    line = line.strip()
    if not line: continue

    if line.startswith('Heading '):
        continue

    data.append(line)

Basically, you don't really need to track a variable for the heading, instead you can just filter out all lines that match the Heading pattern.

Answer 3

Other than a generator, I think we can create a dict where the key is "Heading" and the value is one list to save the lines. Here is the code

odd_map = {}
odd_list = []
with open(file, 'r') as myFile:
    lines = myFile.readlines()
    for line in lines:
        if "Heading" in line:
            odd_list = []
            odd_map[line.strip()] = odd_list
        else:    
            odd_list.append(line.strip())

for company, odds in odd_map.items():
    print(company)
    for odd in odds:
        print(odd)

Answer 4

I don't really know Python, but here's a bit of pseudocode.

int header_found=0;

[start where loop where you're looping through lines of file]

if(header_found==1) [grab line]; header_found=0;

if(line=~/[regexp for header]/) header_found=1;

The idea is to have a variable that keeps track of whether or not you've found a header, and if you have, to grab the next line.