Python -在文件中查找最多4行代码中的模式

Question

我有以下任务。我必须在我的file.txt中找到一个特定的模式(Word)(这是一首以页面为中心的歌曲)，并打印出行号+其中有模式的行，去掉左边的空格。您可以在这里看到正确的输出：

 92 Meant in croaking "Nevermore."
 99 She shall press, ah, nevermore!
107 Quoth the Raven, "Nevermore."
115 Quoth the Raven, "Nevermore."

and without this: my_str += ' '+str(count)+ ' ' + line.lstrip(), it will print:

92 Meant in croaking "Nevermore."
99 She shall press, ah, nevermore!
107 Quoth the Raven, "Nevermore."
115 Quoth the Raven, "Nevermore."

This is my code, but i want to have only 4 lines of code
```python

def find_in_file(模式，文件名)：

my_str = ''

with open(filename, 'r') as file:

    for count,line in enumerate(file):

        if pattern in line.lower():

            if count >= 10 and count <= 99:

                my_str += ' '+str(count)+ ' ' + line.lstrip()

            else:

                my_str += str(count)+ ' ' + line.lstrip()

print(my_str)

Answer 1

实际上，可以完成一行：

''.join(f' {count} {line.lstrip()}' if 10 <= count <= 99 else f'{count} {line.lstrip()}' for count, line in enumerate(file) if pattern in line.lower())

不过，这似乎有点太长了..。

根据评论区，可以简化：

''.join(f'{count:3} {line.lstrip()}' for count, line in enumerate(file) if pattern in line.lower())

Answer 2

def find_in_file(pattern,filename):
    with open(filename, 'r') as file:
        # 0 based line numbering, for 1 based use enumerate(file,1)
        for count,line in enumerate(file):
            if pattern in line.lower():
                print(f"{count:>3} {line.strip()}")

将是4行代码(在函数中)，并且应该与您得到的代码相等。

也有可能在一行：

def find_in_file(pattern,filename):
    # 1 based line numbering
    return '\n'.join(f'{count:>3} {line.strip()}' for count, line in enumerate(file,1) if pattern in line.lower())

见蟒蛇迷你格式语言。

Answer 3

您可以使用格式化字符串来确保数字始终使用三个字符，即使它们只有1或2个数字。

我也更喜欢使用str.strip而不是str.lstrip，以消除尾随空格；特别是，从文件中读取的行通常以换行结束，然后print将添加第二个换行符，如果不去掉它们，我们将得到太多的换行符。

def find_in_file(pattern,filename):
    with open(filename, 'r') as file:
        for count,line in enumerate(file):
            if pattern in line.lower():
                print('{:3d} {}'.format(count, line.strip()))

find_in_file('nevermore','theraven.txt')
#  55 Quoth the Raven "Nevermore."
#  62 With such name as "Nevermore."
#  69 Then the bird said "Nevermore."
#  76 Of 'Never—nevermore'."
#  83 Meant in croaking "Nevermore."
#  90 She shall press, ah, nevermore!
#  97 Quoth the Raven "Nevermore."
# 104 Quoth the Raven "Nevermore."
# 111 Quoth the Raven "Nevermore."
# 118 Quoth the Raven "Nevermore."
# 125 Shall be lifted—nevermore!