14种常见错误

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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)
7



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)
5

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

d = 6
print(d)
6


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'


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