Question

我对python中的索引感到困惑。我使用以下代码从文件中读取一行并打印列表中的第一项。我认为每次读取一行时索引都设置为零。我得到以下代码的索引超出范围。请解释我哪里出错了。

- (BOOL)isValidPhoneNumber:(NSString*)phoneNumber {
    NSDataDetector *detector = [NSDataDetector dataDetectorWithTypes:NSTextCheckingTypePhoneNumber error:nil];
    NSTextCheckingResult *result = [detector firstMatchInString:phoneNumber options:NSMatchingReportCompletion range:NSMakeRange(0, [phoneNumber length])];
    if ([result resultType] == NSTextCheckingTypePhoneNumber) {
        return YES;
    }
    return NO;
}

Answer 1

如果字符串为空，则可能会变坏。

In [1]: line = '     '
In [2]: line = line.strip()
In [4]: b = line.split()
In [5]: b
Out[5]: []
In [6]: b[0]
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-6-422167f1cdee> in <module>()
----> 1 b[0]

IndexError: list index out of range

或许更新您的代码如下：

fname = input("Enter file name: ") 

fh = open(fname)  
for line in fh:     
    line = line.strip()     
    b = line.split()
    if b: 
        print(b[0])

Answer 2

如果line为空（换句话说它只包含空格和回车符），那么在line.strip()之后它将是空字符串。

>>> line = ""
>>> line.split()[0]

Traceback (most recent call last):
  File "<pyshell#50>", line 1, in <module>
    line.split()[0]
IndexError: list index out of range

换句话说，当您对空字符串使用split时，会返回一个空列表。所以没有元素零。

Answer 3

如前所述，如果line为空，则会出现索引错误。

如果你想读行，可能会改变一些你的代码让Python为你做的工作

fname = input("Enter file name: ") 
with open(fname) as f
    lines = f.readlines()
# f will be closed at end of With statement no need to take care
for line in lines:     
    line = line.strip()     
    print(line)      
    # following line may not be used, as line is a String, just access as an array
    #b = line.split()
    print(line[0])

在从文件中读取多行时，在python中索引超出范围

3 个答案: