ValueError: cannot switch from manual field specification to automatic field numbering

Question

class:

class Book(object):
    def __init__(self, title, author):
        self.title = title
        self.author = author

    def get_entry(self):
        return "{0} by {1} on {}".format(self.title, self.author, self.press)

从中创建我的书的实例：

In [72]: mybook = Book('HTML','Lee')
In [75]: mybook.title
Out[75]: 'HTML'
In [76]: mybook.author
Out[76]: 'Lee'

请注意，我没有初始化属性 'self.press'，而是在 get_entry method.Go 之前使用它来输入数据。

mybook.press = 'Murach'
mybook.price = 'download'

到目前为止，我可以用vars

指定所有数据输入

In [77]: vars(mybook)
Out[77]: {'author': 'Lee', 'title': 'HTML',...}

我在 console.When 尝试调用 get_entry 方法时硬输入了很多关于 mybook 的数据，错误报告。

mybook.get_entry()
ValueError: cannot switch from manual field specification to automatic field numbering.

所有这一切都在 console.I 的交互模式下进行，珍惜输入的数据，进一步 pickle mybook 文件中的对象。然而，它是有缺陷的。如何在交互模式下拯救它。或者我必须重新开始。

Answer 1

return "{0} by {1} on {}".format(self.title, self.author, self.press)

那是行不通的。如果指定位置，则必须执行到最后：

return "{0} by {1} on {2}".format(self.title, self.author, self.press)

对于您的情况，最好让 python 自动处理：

return "{} by {} on {}".format(self.title, self.author, self.press)

Answer 2

print ("{0:.1f} and the other no {0:.2f}".format(a,b))

python cannot do both manual and automatic precision handling (field numbering) in a single execution of code. You can either go for specifying the field numbering for each variable or let python do it automatically for all.

Answer 3

好吧，如果可以 table 格式给出正确的输出，如果而不是使用 format go for f"" ;

例如

<!DOCTYPE html>
<html>
<head>
    <title><strong>Unable to handle Value Error</strong></title>
</head>
<body>
<p><ol>for name, branch,year in college:</ol>
         <ol> print(f"{name:{10}} {branch:{20}} {year:{12}} )</ol>
    
    <ol>name       branch               year    </ol>
    <ol>ankit      cse                         2</ol>
    <ol>vijay      ece                         4</ol>
<ol>    raj        IT                          1</ol>

</body>
</html>

ValueError: cannot switch from manual field specification to automatic field numbering

ValueError: cannot switch from manual field specification to automatic field numbering

python

string-formatting

python-3.x