Python异常 ValueError的问题详解

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Python异常 ValueError

ValueError: invalid literal for int() with base 10: '*'

试图将一个与数字无关的类型转化为整数，会抛出该异常。

>>> int("99 years ago.")
Traceback (most recent call last):
  File "", line 1, in 
ValueError: invalid literal for int() with base 10: '99 years ago.'

规避方法：int函数参数应该合法使用。int函数使用传送门：Python中的int函数使用

ValueError: too many values to unpack (expected 2)

试图遍历字典时同时遍历键和值。

>>> demo = {"China": "Beijing", "Japan": "Tokyo"}
>>> for k, v in demo:
...     print(k, v)
...
Traceback (most recent call last):
  File "", line 1, in 
ValueError: too many values to unpack (expected 2)

Python只允许对字典key的遍历，因此上面的遍历方式是错误的。

规避方法

方法一：使用dict[key]的方式同时获取value

>>> demo = {"China": "Beijing", "Japan": "Tokyo"}
>>> for key in demo:
...     print(key, demo[key])
...
China Beijing
Japan Tokyo

方法二：使用items方法

>>> demo = {"China": "Beijing", "Japan": "Tokyo", "the United States": "Washington D.C."}
>>> for key, value in demo.items():
...     print(key, value)
...
China Beijing
Japan Tokyo
the United States Washington D.C.
ValueError: binary mode doesn't take an encoding argument

试图以二进制模式读取文件时指定编码方式。www.linuxprobe.com

>>> with open("protoc-gen-go", "rb+", encoding="utf-8") as file:
...     data = file.read()
...
Traceback (most recent call last):
  File "", line 1, in 
ValueError: binary mode doesn't take an encoding argument

规避方法：避免使用encoding关键字

>>> with open("protoc-gen-go", "rb+") as file:
...     data = file.read(10)
...
>>> data
b'\xcf\xfa\xed\xfe\x07\x00\x00\x01\x03\x00'