How can I read from specific lines in python?

Question

I have an app in python where I'm reading from a plain text.

It's working fine. My question is there is a possible way to read from multiple lines instead of line by line. For example here's is my plain text file color.txt:

###
#####
#########

#example colors
#line of colors
#line colors PART 1
        color1 gray
        color2 blue


# line colors PART 2
iface eth1 inet static
        color1 yellow
        color2 green

I want color1 and color2 from "part1" so I'm reading this line by line but if I change position of color1 for color2 I'm getting an error, so is there a way to read everything inside of "part1" ? that way I can get the same result.

Here's my full code:

from flask import Flask,render_template,flash,request,redirect
import os
import sys
app = Flask(__name__)

def color1_p1():
    with open('color.txt', 'r+') as f:
        for i, line in enumerate(f):
          if i == 7: 
            found_color = line.find('color1')
            if found_color != -1:
               color = line[found_color+len('color1:'):]
               print ('Color: '), color
    return color


def color2_p1():
    with open('color.txt', 'r+') as f:
        for i, line in enumerate(f):
          if i == 8: 
            found_color = line.find('color2')
            if found_color != -1:
               color = line[found_color+len('color2:'):]
               print ('Color: '), color
    return color


def color1_p2():
    with open('color.txt', 'r+') as f:
        for i, line in enumerate(f):
          if i == 13: 
            found_color = line.find('color1')
            if found_color != -1:
               color = line[found_color+len('color1:'):]
               print ('Color: '), color
    return color

def color2_p2():
    with open('color.txt', 'r+') as f:
        for i, line in enumerate(f):
          if i == 14: 
            found_color = line.find('color2')
            if found_color != -1:
               color = line[found_color+len('color2:'):]
               print ('Color: '), color
    return color



@app.route('/')
def showLine():
    color1 = color1_p1()
    color2 = color2_p1()
    color3 =color1_p2()
    color4 = color2_p2()
    return render_template('color.html', color1=color1, color2=color2, color3=color3,color4=color4)

if __name__ == '__main__':
    app.run(debug=True)

as you can see I'm getting the content by lines, I want to read everything inside of part "1" , I tried without the lines but when doing so it will read the "part 2" or the first "color1 and color2" they find.

Here's my output:

All I want is to read color1 or color2 no matter the line it is, if I change the position the program should read this, and same should happen in part 2.

You might be able to use a regular expression to find the "pattern" of color1 — OneCricketeer
– OneCricketeer, Commented Nov 9, 2016 at 4:23

Max Ru · Accepted Answer · 2016-11-09 09:36:17Z

2

#!/usr/lib/env python
import re

file = open("color.txt","r")
content = file.read()
file.close()
content = content.split('PART ')[1:]
dic = {}
for part in content:
    dic[int(part[0])] = part[1:]

def color(color_index, part_index):
    color = re.search('color{_color_index}\s(.*?)\s'.format(_color_index=color_index),dic[part_index]).group(1)
    print 'color',color_index,'of PART',part_index,":",color
    return color

color(1,1)#color 1 of PART 1 : gray
color(2,1)#color 2 of PART 1 : blue
color(1,2)#color 1 of PART 2 : yellow
color(2,2)#color 2 of PART 2 : green

This way, you can get what you want no matter how parts and colors are arranged.

answered Nov 9, 2016 at 9:36

Max Ru

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6 Comments

Alvaro E Over a year ago

Is there a possible way to make it work without the index 1 or 2? for example with only the word "color" in my plain text? @Max

Max Ru Over a year ago

You can get all colors appeared in your text by colors = re.findall('color\d\s(.*?)\s',open('color.txt','r').read()) if you don't care the index of colors and parts. Or by colors = re.findall('color\d\s(.*?)\s',dic[part_index]) if you want them found corresponding to parts. And I think you'd better learn some fundamental knowledge on regular expression, which helps a lot when you wanna find specific string in a text file.

Alvaro E Over a year ago

I tried color = re.findall('color\d\s(.*?)\s',dic[part_index]) because I want them by parts and I got the following result by console [ ] which should be red instead? @Max

Max Ru Over a year ago

I test it with color.txt you provided above, and get ['gray', 'blue'] and ['yellow', 'green'] as results of color(1) and color(2) respectively. So I think the format of you current text file may be different from the one you provided above? Coz the regex 'color\d\s(.*?)\s' find strings organized exactly like color\d\sred\s, where \d represents a digit, \s represents a whitespace character. So if your text format changes, make sure you write proper regular expression to match them. Here is a link to document of re lib [docs.python.org/2/library/re.html] @pythonbegineer

Alvaro E Over a year ago

Thanks for you answer! yes I have the same result as you have, but I meant I got ['gray' , 'blue'] and ['yellow', 'green'] as results of color(1) and color(2). But in the first answer you I got the four colors in four results as color(1), color(2),color(3) and finally color(4). I would like to have something like that. for example instead of print color(1) and get ['gray' , 'blue'] I would like to print color(1) and get 'gray' after that color(2) and get 'blue'. That's all I need. Is that possible? . By the way the link didn't work. Thanks..! @Max

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