如何检测在 Python 中打开的文件的每一行中的第一个非空白字符？

Question

我正在尝试编写 Python 代码来检测文件中每一行中的第一个非空白字符并检查它是否是“}”。 例如，如果我的文件内容是...

a
fox {
  }
{ jumped
} up

...我想检测第三行中的“}”，尽管它有两个空格，并且在第五行。

我试过做这样的事情，但我被困住了：

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()

非常感谢帮助！

Answer 1

您可以尝试在每一行调用strip() ，然后只检查第一个字符：

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

您可以使用此 function 来获取第一个非空白字符。

这一次只读取一行，因此如果您正在处理一个非常大的文件，它可以为您节省一些麻烦。

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

尝试使用这样的文件：

sample.txt

     }hello

使用 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

我的版本略有不同的输入（sample.txt 末尾有两个空行，'\n'）：

a
fox {
  }
{ jumped


} up

是：

#!/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 :  }