初學Python常見錯誤
- 忘記寫冒號
- 誤用=
- 錯誤 縮緊
- 變量沒有定義
- 中英文輸入法導致的錯誤
- 不同數據類型的拼接
- 索引位置問題
- 使用字典中不存在的鍵
- 忘了括號
- 漏傳參數
- 缺失依賴庫
- 使用了python中對關鍵詞
- 編碼問題
1. 忘記寫冒號
在 if、elif、else、for、while、def語句後面忘記添加 :
age = 42
if age == 42
print('Hello!')
File "<ipython-input-19-4303141d6f97>", line 2
if age == 42
^
SyntaxError: invalid syntax
2. 誤用 =
=` 是賦值操作,而判斷兩個值是否相等是 `==
gender = '男'
if gender = '男':
print('Man')
File "<ipython-input-20-191d01f95984>", line 2
if gender = '男':
^
SyntaxError: invalid syntax
3. 錯誤的縮進
Python用縮進區分代碼塊,常見的錯誤用法:
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. 變量沒有定義
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. 中英文輸入法導致的錯誤
- 英文冒號
- 英文括號
- 英文逗號
- 英文單雙引號
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. 不同數據類型的拼接
字符串/列表/元組 支持拼接
字典/集合不支持拼接
#小編創建了一個Python學習交流QQ羣:857662006
'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. 索引位置問題
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鍵
在字典對象中訪問 key 可以使用 []
,
但是如果該 key 不存在,就會導致: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'
爲了避免這種情況,可以使用 get 方法
spam = {'cat': 'Zophie',
'dog': 'Basil',
'mouse': 'Whiskers'}
print(spam.get('zebra'))
None
key 不存在時,get 默認返回 None
9. 忘了括號
當函數中傳入的是函數或者方法時,容易漏寫括號
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. 漏傳參數
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. 缺失依賴庫
電腦中沒有相關的庫
12. 使用了python中的關鍵詞
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. 文件編碼問題
import pandas as pd
df = pd.read_csv('data/twitter情感分析數據集.csv')
df.head()
嘗試encoding編碼參數傳入utf-8、gbk
df = pd.read_csv('data/twitter情感分析數據集.csv', encoding='utf-8')
df.head()
都報錯說明編碼不是utf-8和gbk,而是不常見都編碼,這裏我們需要傳入正確都encoding,才能讓程序運行。
python有個chardet庫,專門用來偵測編碼。
import chardet
binary_data = open('data/twitter情感分析數據集.csv', 'rb').read()
chardet.detect(binary_data)
{'encoding': 'Windows-1252', 'confidence': 0.7291192008535122, 'language': ''