How to Change Style of a Title with Python-Docx?

I'm using python-docx but I don't understand or retrieve any way to change the style (from bold to normal) of the title. My code is:

import docx
from docx.shared import RGBColor
from docx.shared import Pt
from docx.dml.color import ColorFormat
from docx.enum.style import WD_STYLE_TYPE

#format only the filename as return text
def format_filename(fname):
    index = fname.rfind('\\')
    font.color.rgb = RGBColor(255,0,0)
    #IF statement for structuring the fine name
    if index>0:
        filename = fname[index + 1, len(fname)]
    else:
        index = fname.rfind('/')
        filename = fname[index + 1 : len(fname)]
    return filename

#print all the file into docx
def print_file(file):
    font.bold = False
    font.color.rgb = RGBColor(0,0,0)
    cnt = 0
    fp = open(file, 'r')
    #read all the file and use every single line
    for line in fp.readlines():
        cnt += 1
        #if it's the first line add paragraph
        if cnt == 1:
            paragraph = document.add_paragraph(line)
        #else continue the paragraph
        else:
            paragraph.add_run(line)

#open file
document = docx.Document()
filepath = '../cap1/prg1.txt'

# set the font in the paragraph
run = document.add_paragraph().add_run()
style = document.styles['Normal']
font = style.font
font.name = 'Courier New'
font.size = Pt(10.5)
font.bold = True
font.color.rgb = RGBColor(255,0,0)

#print as a heading the filename
filename = format_filename(filepath) #self procedure for format the filename
document.add_heading(filename , level=2)
#print all the file
print_file(filepath)

document.save('my_cake_file.docx')

Here is how the title looks like after coloring: