在列表中查找字符索引

Question

我想在 .txt 文件中搜索某个字符 (X)，如果存在，则执行某个操作。不幸的是这段代码不起作用：file = "test.txt"file = open(file, "r") lines = file.readlines()# char in the listif "X" in lines:    print('X is present in the list')# char not in the listif "X" not in lines:    print('X is not present in the list')测试.txt 文件：XX X XXX X XXXXXXX XX X    XX有什么想法吗？PS：即使将“X”更改为“X”也不起作用。

Answer 1

如果您需要知道X出现的行号：

target = 'X'

counter = 0

with open('testing.txt') as f:

    for i, line in enumerate(f):

        if target in line:

            counter += 1

            print('target is present in line {}'.format(

                i+1))

print('target appears in {} lines'.format(counter))

如果您还需要知道X出现的列号：

target = 'X'

counter = 0

with open('testing.txt') as f:

    for i, line in enumerate(f):

        for j, char in enumerate(line):

            if target == char:

                counter += 1

                print('target is present in line {} at column {}'.format(

                    i+1, j+1))

print('target appears {} times'.format(counter))

一些澄清：

• with ... open完成后自动关闭文件，因此您无需记住显式关闭它

• for i, line in enumerate(f):逐行迭代，而不将它们一次性全部加载到内存中。

Answer 2

由于readlines()是一个列表，您需要迭代并签入行。也许您可以用于for else此目的：

file = "testing.txt"

file = open(file, "r") 

lines = file.readlines()

# char in the list

for line in lines:

    if "X" in line:

        print('X is present in the list')

        break

else:

    print('X is not present in the list')

它迭代每一行，如果任何行有字符，则break仅else在任何行中都找不到字符时才运行。

更新

如果你想计数，那么你可以简单地在循环中增加计数器，一旦循环完成检查计数器：

file = "testing.txt"

file = open(file, "r") 

lines = file.readlines()

# char in the list

counter = 0

for line in lines:

    if "X" in line:

        counter += 1  # < -- count

        

if counter: # check    

    print('X is present in the list')

        

else:

    print('X is not present in the list') 

Answer 3

正如您所要求的，我将输出一个包含 item 的列表Yes, there are 3 X's。

我有我的dataf.txt文件：

XXX X XX X XX

X ASD X F FFFF XX

D X XXX X EFX

A F G

将数据读入文件并计算 X 的数量（注意：我使用了列表理解 hack！）

with open('dataf.txt','r') as fl:

    data = fl.readlines()

    a = ['Yes, there are '+str(i.count('X')) + " X's" if 'X' in i else "No X's" for i in data]

    print(a)

输出：

["Yes, there are 9 X's", "Yes, there are 4 X's", "Yes, there are 6 X's", "No X's"]