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

'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': ''