初学Python常见异常错误，总有一处你会遇到！
初学Python常见错误
- 忘记写冒号
- 误用=
- 错误 缩紧
- 变量没有定义
- 中英文输入法导致的错误
- 不同数据类型的拼接
- 索引位置问题
- 使用字典中不存在的键
- 忘了括号
- 漏传参数
- 缺失依赖库
- 使用了python中对关键词
- 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': ''
