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，请执行某个操作。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 list
if "X" in lines:
    print('X is present in the list')

# char not in the list
if "X" not in lines:
    print('X is not present in the list')

test.txt 文件：

XX X XXX X XX
XXXXX XX X    XX

有什么想法吗？

P.S.：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 完成后会自动关闭文件，因此您无需记住显式关闭它
• for i, line in enumerate(f): 逐行迭代，而不是一次将它们全部加载到内存中。

Answer 2

由于readlines() 是一个列表，您需要迭代并签入行。也许您可以为此使用for else：

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')

它遍历每一行，如果任何行有字符break，则调用else，只有在任何行中都找不到字符时才会运行。

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

正如你所问的，我将输出一个带有项目Yes, there are 3 X's 的列表。

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：我使用了列表理解技巧！）

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"]