Parse a porcelain output from git diff

parse_porcelain.py

import re

css_add = """
.add{                                 
  background-color:rgba(0, 255, 0, .2); 
}                                     
.remove{                              
  background-color:rgba(255, 0, 0, .2); 
  color:black;                          
}                           
"""

def am_I_inside_a_tag(line):
    match = re.match( r'^[^<]*>', line)
    match2 = re.match( r'<[^>]*$', line)
    if match or match2:
        return True
    else:
        return False

def main():
    # read file
    with open("diff.html") as f:
        content = f.readlines()

    # output
    output_html = ""
        
    # detect head
    still_in_head = True

    # line by line
    for line in content:

        # parse porcelain output
        if line[0] == "~":
            output_html += "\n"
        elif line[0] == " ":
            output_html += line[1:-1]
            if line[1:7] == "<style":
                output_html += css_add
        elif line[0] == "+":
            if not still_in_head and not am_I_inside_a_tag(line):
                output_html += "<span class=\"add\">" + line[1:-1] + "</span>"
            else:
                output_html += line[1:-1]
        elif line[0] == "-":
            if not still_in_head and not am_I_inside_a_tag(line):
                output_html += "<span class=\"remove\">" + line[1:-1] + "</span>"
        else:
            print "error"
            break

        # am I inside a tag?
        if line[1:8] == "</head>":
            still_in_head = False

    # print output
    print output_html

if __name__ == "__main__":
    main()