python identifier expected_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 "", 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 "", 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 "", line 2
print('howdy!')
^
indentationerror: unexpected indent
num = 25
if num == 25:
print('hello!')
file "", 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)
in
----> 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 "", line 1
if 5>3：
^
syntaxerror: invalid character in identifier
if 5>3:
print('5比3大')
file "", line 2
print('5比3大')
^
syntaxerror: invalid character in identifier
spam = [1, 2，3]
file "", line 1
spam = [1, 2，3]
^
syntaxerror: invalid character in identifier
if 5>3:
print('5比3大‘)
file "", 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)
in
----> 1 'i have ' + 12 + ' eggs.'
typeerror: can only concatenate str (not "int") to str
['a', 'b', 'c']+'def'
---------------------------------------------------------------------------
typeerror traceback (most recent call last)
in
----> 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)
in
----> 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)
in
----> 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)
in
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)
in
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)
in
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 "", 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)
in
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 "", line 1
try = 5
^
syntaxerror: invalid syntax
def = 6
print(6)
file "", 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': ''
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