初学Python常见异常错误，总有一处你会遇到！

初学Python常见错误

1. 忘记写冒号
2. 误用=
3. 错误 缩紧
4. 变量没有定义
5. 中英文输入法导致的错误
6. 不同数据类型的拼接
7. 索引位置问题
8. 使用字典中不存在的键
9. 忘了括号
10. 漏传参数
11. 缺失依赖库
12. 使用了python中对关键词
13. 编码问题

1. 忘记写冒号

在 if、elif、else、for、while、def语句后面忘记添加 :

age = 42 if age == 42 print('Hello!') File "<ipython-input-19-4303141d6f97>", line 2 if age == 42 ^ SyntaxError: invalid syntax

2. 误用 =

=` 是赋值操作，而判断两个值是否相等是 `== gender = '男' if gender = '男': print('Man') File "<ipython-input-20-191d01f95984>", line 2 if gender = '男': ^ SyntaxError: invalid syntax

3. 错误的缩进

Python用缩进区分代码块，常见的错误用法：

print('Hello!') print('Howdy!') File "<ipython-input-9-784bdb6e1df5>", line 2 print('Howdy!') ^ IndentationError: unexpected indent num = 25 if num == 25: print('Hello!') File "<ipython-input-21-8e4debcdf119>", line 3 print('Hello!') ^ IndentationError: expected an indented block

4. 变量没有定义

 if city in ['New York', 'Bei Jing', 'Tokyo']: print('This is a mega city') --------------------------------------------------------------------------- NameError Traceback (most recent call last) <ipython-input-22-a81fd2e7a0fd> in <module> ----> 1 if city in ['New York', 'Bei Jing', 'Tokyo']: 2 print('This is a mega city') NameError: name 'city' is not defined

5. 中英文输入法导致的错误

• 英文冒号
• 英文括号
• 英文逗号
• 英文单双引号

if 5>3： print('5比3大') File "<ipython-input-46-47f8b985b82d>", line 1 if 5>3： ^ SyntaxError: invalid character in identifier if 5>3: print('5比3大'） File "<ipython-input-47-4b1df4694a8d>", line 2 print('5比3大'） ^ SyntaxError: invalid character in identifier spam = [1, 2，3] File "<ipython-input-45-47a5de07f212>", line 1 spam = [1, 2，3] ^ SyntaxError: invalid character in identifier if 5>3: print('5比3大‘) File "<ipython-input-48-ae599f12badb>", line 2 print('5比3大‘) ^ SyntaxError: EOL while scanning string literal

6. 不同数据类型的拼接

字符串/列表/元组 支持拼接

字典/集合不支持拼接

#小编创建了一个Python学习交流QQ群：857662006 'I have ' + 12 + ' eggs.' #'I have {} eggs.'.format(12) --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-29-20c7c89a2ec6> in <module> ----> 1 'I have ' + 12 + ' eggs.' TypeError: can only concatenate str (not "int") to str ['a', 'b', 'c']+'def' --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-31-0e8919333d6b> in <module> ----> 1 ['a', 'b', 'c']+'def' TypeError: can only concatenate list (not "str") to list ('a', 'b', 'c')+['a', 'b', 'c'] --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-33-90742621216d> in <module> ----> 1 ('a', 'b', 'c')+['a', 'b', 'c'] TypeError: can only concatenate tuple (not "list") to tuple set(['a', 'b', 'c'])+set(['d', 'e']) --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-35-ddf5fb1e6c8c> in <module> ----> 1 set(['a', 'b', 'c'])+set(['d', 'e']) TypeError: unsupported operand type(s) for +: 'set' and 'set' grades1 = {'Mary':99, 'Henry':77} grades2 = {'David':88, 'Unique':89} grades1+grades2 --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-36-1b1456844331> in <module> 2 grades2 = {'David':88, 'Unique':89} 3 ----> 4 grades1+grades2 TypeError: unsupported operand type(s) for +: 'dict' and 'dict'

7. 索引位置问题

spam = ['cat', 'dog', 'mouse'] print(spam[5]) --------------------------------------------------------------------------- IndexError Traceback (most recent call last) <ipython-input-38-e0a79346266d> in <module> 1 spam = ['cat', 'dog', 'mouse'] ----> 2 print(spam[5]) IndexError: list index out of range

8. 使用字典中不存在的键

在字典对象中访问 key 可以使用 []，

但是如果该 key 不存在，就会导致：KeyError: 'zebra'

spam = {'cat': 'Zophie', 'dog': 'Basil', 'mouse': 'Whiskers'} print(spam['zebra']) --------------------------------------------------------------------------- KeyError Traceback (most recent call last) <ipython-input-39-92c9b44ff034> in <module> 3 'mouse': 'Whiskers'} 4 ----> 5 print(spam['zebra']) KeyError: 'zebra'

为了避免这种情况，可以使用 get 方法

spam = {'cat': 'Zophie', 'dog': 'Basil', 'mouse': 'Whiskers'} print(spam.get('zebra')) None

key 不存在时，get 默认返回 None

9. 忘了括号

当函数中传入的是函数或者方法时，容易漏写括号

spam = {'cat': 'Zophie', 'dog': 'Basil', 'mouse': 'Whiskers'} print(spam.get('zebra') File "<ipython-input-43-100a51a7b630>", line 5 print(spam.get('zebra') ^ SyntaxError: unexpected EOF while parsing

10. 漏传参数

def diyadd(x, y, z): return x+y+z diyadd(1, 2) --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-44-7184f3f906ca> in <module> 2 return x+y+z 3 ----> 4 diyadd(1, 2) TypeError: diyadd() missing 1 required positional argument: 'z'

11. 缺失依赖库

电脑中没有相关的库

12. 使用了python中的关键词

如try、except、def、class、object、None、True、False等

try = 5 print(try) File "<ipython-input-1-508e87fe2ff3>", line 1 try = 5 ^ SyntaxError: invalid syntax def = 6 print(6) File "<ipython-input-2-d04205303265>", line 1 def = 6 ^ SyntaxError: invalid syntax

13. 文件编码问题

import pandas as pd df = pd.read_csv('data/twitter情感分析数据集.csv') df.head()

尝试encoding编码参数传入utf-8、gbk

df = pd.read_csv('data/twitter情感分析数据集.csv', encoding='utf-8') df.head()

都报错说明编码不是utf-8和gbk，而是不常见都编码，这里我们需要传入正确都encoding，才能让程序运行。

python有个chardet库，专门用来侦测编码。

import chardet binary_data = open('data/twitter情感分析数据集.csv', 'rb').read() chardet.detect(binary_data) {'encoding': 'Windows-1252', 'confidence': 0.7291192008535122, 'language': ''