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 :

1. age = 42

2. if age == 42

3. print('Hello!')

1. File"", line 2

2. if age == 42

3. ^

4. SyntaxError: invalid syntax

2. 误用 =

= 是赋值操作，而判断两个值是否相等是 ==

1. gender = '男'

2. if gender = '男':

3. print('Man')

1. File"", line 2

2. if gender = '男':

3. ^

4. 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：

1. print('Hello!')

2. print('Howdy!')

1. File"", line 2

2. print('Howdy!')

3. ^

4. IndentationError: unexpected indent

1. num = 25

2. if num == 25:

3. print('Hello!')

1. File"", line 3

2. print('Hello!')

3. ^

4. IndentationError: expected an indented block

4. 变量没有定义

1. if city in ['New York', 'Bei Jing', 'Tokyo']:

2. print('This is a mega city')

1. ---------------------------------------------------------------------------

2. 
   

3. NameErrorTraceback (most recent call last)

4. 
   

5. 22-a81fd2e7a0fd> in

6. ----> 1if city in ['New York', 'Bei Jing', 'Tokyo']:

7. 2print('This is a mega city')

1. NameError: name 'city'isnotdefined

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

1. if5>3：

2. print('5比3大')

1. File"", line 1

2. if5>3：

3. ^

4. SyntaxError: invalid character in identifier

1. if5>3:

2. print('5比3大'）

1. File"", line 2

2. print('5比3大'）

3. ^

4. SyntaxError: invalid character in identifier

1. spam = [1, 2，3]

1. File"", line 1

2. spam = [1, 2，3]

3. ^

4. SyntaxError: invalid character in identifier

1. if5>3:

2. print('5比3大‘)

1. File"", line 2

2. print('5比3大‘)

3. ^

4. 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

1. 'I have ' + 12 + ' eggs.'

2. #'I have {} eggs.'.format(12)

1. ---------------------------------------------------------------------------

2. 
   

3. TypeErrorTraceback (most recent call last)

4. 
   

5. 29-20c7c89a2ec6> in

6. ----> 1'I have ' + 12 + ' eggs.'

1. TypeError: can only concatenate str (not"int") to str

1. ['a', 'b', 'c']+'def'

1. ---------------------------------------------------------------------------

2. 
   

3. TypeErrorTraceback (most recent call last)

4. 
   

5. 31-0e8919333d6b> in

6. ----> 1 ['a', 'b', 'c']+'def'

1. TypeError: can only concatenate list (not"str") to list

1. ('a', 'b', 'c')+['a', 'b', 'c']

1. ---------------------------------------------------------------------------

2. 
   

3. TypeErrorTraceback (most recent call last)

4. 
   

5. 33-90742621216d> in

6. ----> 1 ('a', 'b', 'c')+['a', 'b', 'c']

1. TypeError: can only concatenate tuple (not"list") to tuple

1. set(['a', 'b', 'c'])+set(['d', 'e'])

1. ---------------------------------------------------------------------------

2. 
   

3. TypeErrorTraceback (most recent call last)

4. 
   

5. 35-ddf5fb1e6c8c> in

6. ----> 1set(['a', 'b', 'c'])+set(['d', 'e'])

1. TypeError: unsupported operand type(s) for +: 'set'and'set'

1. grades1 = {'Mary':99, 'Henry':77}

2. grades2 = {'David':88, 'Unique':89}

3. 
   

4. grades1+grades2

1. ---------------------------------------------------------------------------

2. 
   

3. TypeErrorTraceback (most recent call last)

4. 
   

5. 36-1b1456844331> in

6. 2 grades2 = {'David':88, 'Unique':89}

7. 3

8. ----> 4 grades1+grades2

1. TypeError: unsupported operand type(s) for +: 'dict'and'dict'

7. 索引位置问题

1. spam = ['cat', 'dog', 'mouse']

2. print(spam[5])

1. ---------------------------------------------------------------------------

2. 
   

3. IndexErrorTraceback (most recent call last)

4. 
   

5. 38-e0a79346266d> in

6. 1 spam = ['cat', 'dog', 'mouse']

7. ----> 2print(spam[5])

1. 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'

1. spam = {'cat': 'Zophie',

2. 'dog': 'Basil',

3. 'mouse': 'Whiskers'}

4. 
   

5. print(spam['zebra'])

1. ---------------------------------------------------------------------------

2. 
   

3. KeyErrorTraceback (most recent call last)

4. 
   

5. 39-92c9b44ff034> in

6. 3'mouse': 'Whiskers'}

7. 4

8. ----> 5print(spam['zebra'])

1. KeyError: 'zebra'

为了避免这种情况，可以使用 get 方法

1. spam = {'cat': 'Zophie',

2. 'dog': 'Basil',

3. 'mouse': 'Whiskers'}

4. 
   

5. print(spam.get('zebra'))

1. 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

1. spam = {'cat': 'Zophie',

2. 'dog': 'Basil',

3. 'mouse': 'Whiskers'}

4. 
   

5. print(spam.get('zebra')

1. File"", line 5

2. print(spam.get('zebra')

3. ^

4. SyntaxError: unexpected EOF while parsing

10. 漏传参数

1. def diyadd(x, y, z):

2. return x+y+z

3. 
   

4. diyadd(1, 2)

1. ---------------------------------------------------------------------------

2. 
   

3. TypeErrorTraceback (most recent call last)

4. 
   

5. 44-7184f3f906ca> in

6. 2return x+y+z

7. 3

8. ----> 4 diyadd(1, 2)

1. 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

1. try = 5

2. print(try)

1. File"", line 1

2. try = 5

3. ^

4. SyntaxError: invalid syntax

1. def = 6

2. print(6)

1. File"", line 1

2. def = 6

3. ^

4. SyntaxError: invalid syntax

13. 文件编码问题

1. import pandas as pd

2. 
   

3. df = pd.read_csv('data/twitter情感分析数据集.csv')

4. df.head()

尝试encoding编码参数传入utf-8、gbk

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

2. 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。

1. import chardet

2. 
   

3. binary_data = open('data/twitter情感分析数据集.csv', 'rb').read()

4. chardet.detect(binary_data)

1. {'encoding': 'Windows-1252', 'confidence': 0.7291192008535122, 'language': ''}