How can I detect the first non-whitespace character in each line of a file opened in Python?

Question

I'm trying to write Python code to detect the first non-whitespace character in each line in a file and check if it is a "}". For example, if the contents of my file are...

a
fox {
  }
{ jumped
} up

... I'd want to detect the "}" in the third line despite it having two whitespaces, and in the fifth line.

I've tried doing something like this but I'm stuck:

full_file = open ("filename", "r")
each_line = full_file.readlines()
for item in each_line
  if item[0].find('}') != -1:
    # do something, such as print (item)
full_file.close()

Help much appreciated!

Answer 1

You may try calling strip() on each line, then checking just the first character:

full_file = open ("filename", "r")
each_line = full_file.readlines()
for item in each_line
    if item.strip() and item.strip()[0] == '}':
        print(item)
full_file.close()

Answer 2

You could use this function to get the first non whitespace character.

This only reads one line at a time, so it could save you some trouble if you're dealing with a very large file.

def get_first_non_whitespace_char(file_name):
    with open(file_name, 'r') as fileobj:
        for line in fileobj:  
            for character in line:
                if character != " ":
                    return character
    return None

Trying out with a file like this:

sample.txt

     }hello

Using the function

file_name = "sample.txt"

first_nsp_char = get_first_non_whitespace_char(file_name)

if first_nsp_char != None:
    print("First Non space character in file:", first_nsp_char)
    print("Character is '}' :", first_nsp_char == '}')
else:
    print("No non-whitespace characters found in file:", file_name)

Output:

First Non space character in file: }
Character is '}' : True

Answer 3

my version on slight different input (sample.txt has two empty lines at the end, '\n'):

a
fox {
  }
{ jumped


} up

is:

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Thu Jun 10 11:28:29 2021

@author: Pietro

https://stackoverflow.com/questions/67733277/how-can-i-detect-the-first-non-whitespace-character-in-each-line-of-a-file-opene/67733429#67733429

"""

def get_first_non_whitespace_char(file_name):
    listz ={}
    index = 0
    with open(file_name, 'r') as fileobj:
        for line in fileobj:
            index += 1
            #print('line: ',line)
            for character in line:
                if character != " " and character != '\n':
                    listz[index] = character
                    # index += 1
                    break
                else:
                    pass
    return listz


file_name = "sample.txt"

first_nsp_char = get_first_non_whitespace_char(file_name)

for i in first_nsp_char:
      print('line # ',i,'  first character is : ',first_nsp_char[i])

output:

line #  1   first character is :  a
line #  2   first character is :  f
line #  3   first character is :  }
line #  4   first character is :  {
line #  7   first character is :  }