python常见错误及解决办法

14种常见错误

Python语法入门-课件下载

链接: https://pan.baidu.com/s/1h1RuWimLicVanK8xCka_xA 提取码: x264

学习编程就是在遇到错误、认识错误、解决错误的过程。遇到错误，大家要发挥主观能动性，用自己的英文阅读能力去先读一下英文报错提示，一般情况下错误提示会告诉你是什么类型的错误，错误出在哪一行。

再结合百度谷歌，80%以上的问题都能解决。现在我们了解一下常见的问题都有哪些，如何克服这些问题。

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-10-1f5acea116cf>", line 3
    if age == 42
                ^
SyntaxError: invalid syntax

age = 42

if age == 42:
    print('Hello!')

Hello!

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-12-c3ceea5a9004>", line 3
    if gender = '男':
              ^
SyntaxError: invalid syntax

gender = '男'

if gender == '男':
    print('Man')

Man

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-14-784bdb6e1df5>", line 2
    print('Howdy!')
    ^
IndentationError: unexpected indent

print('Hello!')
print('Howdy!')

Hello!
Howdy!

num = 25
if num == 25:
print('Hello!')

  File "<ipython-input-16-8e4debcdf119>", line 3
    print('Hello!')
        ^
IndentationError: expected an indented block

num = 25
if num == 25:
    print('Hello!')

Hello!

4. 变量没有定义

if c in ['New York', 'Bei Jing', 'Tokyo']:
    print('This is a mega city')

---------------------------------------------------------------------------

NameError                                 Traceback (most recent call last)

<ipython-input-21-d91d0b36da73> in <module>
----> 1 if c in ['New York', 'Bei Jing', 'Tokyo']:
      2     print('This is a mega c')


NameError: name 'c' is not defined

city ='New York'
if city in ['New York', 'Bei Jing', 'Tokyo']:
    print('This is a mega city')

This is a mega city

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-23-47f8b985b82d>", line 1
    if 5>3：
          ^
SyntaxError: invalid character in identifier

if 5>3:
    print('5比3大')

5比3大

spam = [1, 2， 3]

  File "<ipython-input-26-a003060d051a>", line 1
    spam = [1, 2， 3]
                ^
SyntaxError: invalid character in identifier

spam = [1, 2, 3]
spam

[1, 2, 3]

if 5>3:
    print('5比3大’)

  File "<ipython-input-30-ac2e4eb87092>", line 2
    print('5比3大’)
                 ^
SyntaxError: EOL while scanning string literal

if 5>3:
    print('5比3大')

5比3大

6. 不同数据类型的拼接

同种数据类型 字符串/列表/元组 支持拼接

字典/集合不支持拼接

'I have ' + 12 + ' eggs.'

---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

<ipython-input-32-20c7c89a2ec6> in <module>
----> 1 'I have ' + 12 + ' eggs.'


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

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

'I have 12 eggs.'

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

---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

<ipython-input-35-0e8919333d6b> 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-36-90742621216d> 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-37-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-38-1b1456844331> 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-41-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-42-92c9b44ff034> 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')  #end of funtion

  File "<ipython-input-44-d105cc86097c>", line 5
    print(spam.get('zebra')  #end of funtion
                                            ^
SyntaxError: unexpected EOF while parsing

spam = {'cat': 'Zophie', 
        'dog': 'Basil', 
        'mouse': 'Whiskers'}

print(spam.get('zebra'))

None

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-46-7184f3f906ca> in <module>
      2     return x+y+z
      3 
----> 4 diyadd(1, 2)


TypeError: diyadd() missing 1 required positional argument: 'z'

diyadd(1, 2, 4)

11. 缺失依赖库

电脑中没有相关的库

import packagename

---------------------------------------------------------------------------

ModuleNotFoundError                       Traceback (most recent call last)

<ipython-input-48-6d7d6f569116> in <module>
----> 1 import packagename


ModuleNotFoundError: No module named 'packagename'

!pip install packagename

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-49-508e87fe2ff3>", line 1
    try = 5
        ^
SyntaxError: invalid syntax

a = 5
print(a)

def = 6
print(def)

  File "<ipython-input-51-c797890e9b85>", line 1
    def = 6
        ^
SyntaxError: invalid syntax

d = 6
print(d)

13. 文件编码问题

import pandas as pd

df = pd.read_csv('data/twitter_sentiment.csv')
df.head()

UnicodeDecodeError: 'utf-8' codec can't decode bytes in position 7-8: invalid continuation byte
UnicodeDecodeError                        Traceback (most recent call last)

<ipython-input-53-f7ee81cff3e5> in <module>
      1 import pandas as pd
      2 
----> 3 df = pd.read_csv('data/twitter_sentiment.csv')
      4 df.head()
pandas\_libs\parsers.pyx in pandas._libs.parsers._string_box_utf8()
UnicodeDecodeError: 'utf-8' codec can't decode bytes in position 7-8: invalid continuation byte

import pandas as pd

#gbk/utf-8只能解决大部分编码问题，但不能解决全部问题
df = pd.read_csv('data/twitter_sentiment.csv', encoding='gbk')
df.head()

---------------------------------------------------------------------------

UnicodeDecodeError                        Traceback (most recent call last)

<ipython-input-55-6aa161f42239> in <module>
      2 
      3 #gbk/utf-8只能解决大部分编码问题，但不能解决全部问题
----> 4 df = pd.read_csv('data/twitter_sentiment.csv', encoding='gbk')
      5 df.head()


c:\users\thunderhit\appdata\local\programs\python\python37-32\lib\site-packages\pandas\io\parsers.py in parser_f(filepath_or_buffer, sep, delimiter, header, names, index_col, usecols, squeeze, prefix, mangle_dupe_cols, dtype, engine, converters, true_values, false_values, skipinitialspace, skiprows, skipfooter, nrows, na_values, keep_default_na, na_filter, verbose, skip_blank_lines, parse_dates, infer_datetime_format, keep_date_col, date_parser, dayfirst, cache_dates, iterator, chunksize, compression, thousands, decimal, lineterminator, quotechar, quoting, doublequote, escapechar, comment, encoding, dialect, error_bad_lines, warn_bad_lines, delim_whitespace, low_memory, memory_map, float_precision)
    674         )
    675 
-> 1891         self._reader = parsers.TextReader(src, **kwds)
   1892         self.unnamed_cols = self._reader.unnamed_cols
   1893 
   pandas\_libs\parsers.pyx in pandas._libs.parsers.TextReader.__cinit__()
	pandas\_libs\parsers.pyx in pandas._libs.parsers.TextReader._get_header()
	pandas\_libs\parsers.pyx in pandas._libs.parsers.TextReader._tokenize_rows()
	pandas\_libs\parsers.pyx in pandas._libs.parsers.raise_parser_error()
	UnicodeDecodeError: 'gbk' codec can't decode byte 0xbd in position 10717: 	illegal multibyte sequence

上面的程序会提示编码错误，尝试encoding编码参数传入utf-8、gbk，也没有解决问题。

那怎么找到正确的编码参数呢？

import chardet

#读取为二进制数据
binary_data = open('data/twitter_sentiment.csv', 'rb').read()

#传给chardet.detect，稍等片刻
chardet.detect(binary_data)

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

import pandas as pd


df = pd.read_csv('data/twitter_sentiment.csv', encoding='Windows-1252')
df.head()

	ItemID	Sentiment	SentimentText
0	1	0	is so sad for my APL frie...
1	2	0	I missed the New Moon trail...
2	3	1	omg its already 7:30 :O
3	4	0	.. Omgaga. Im sooo im gunna CRy. I'...
4	5	0	i think mi bf is cheating on me!!! ...

14. 路径字符串写法

Mac&Win 推荐使用 / 写法
如果使用\ 写法，安全起见，请换成\\ （Mac不支持\\ ）

\n
\t
\d

open('data/test.txt', encoding='utf-8').read()

'章节设计\n\n第一部分  环境配置\n第二部分  快速入门python\n第三部分  网络爬虫\n第四部分  简单的文本分析\n第五部分  进阶文本分析'

open('data\test.txt', encoding='utf-8').read()

---------------------------------------------------------------------------

OSError                                   Traceback (most recent call last)

<ipython-input-59-d855ed58b500> in <module>
----> 1 open('data\test.txt', encoding='utf-8').read()


OSError: [Errno 22] Invalid argument: 'data\test.txt'

open('data\\test.txt', encoding='utf-8').read()

'章节设计\n\n第一部分  环境配置\n第二部分  快速入门python\n第三部分  网络爬虫\n第四部分  简单的文本分析\n第五部分  进阶文本分析'

open('data\Test.txt', encoding='utf-8').read()

'章节设计\n\n第一部分  环境配置\n第二部分  快速入门python\n第三部分  网络爬虫\n第四部分  简单的文本分析\n第五部分  进阶文本分析'

了解课程

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14种常见错误#

Python语法入门-课件下载#

1. 忘记写冒号#

2. 误用 =#

3. 错误的缩进#

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中的关键词#

13. 文件编码问题#

那怎么找到正确的编码参数呢？#

14. 路径字符串写法#

了解课程#