《Python 3 面向对象编程》学习笔记 - 常见错误提示

NameError: name ‘Xxx’ is not defined

示例 0：

>>> stus=['x','=',2,y]   #不需声明，直接赋值
Traceback (most recent call last):
  File "", line 1, in <module>
    stus=['x','=',2,y]
NameError: name 'y' is not defined

示例 1：

import datetime
last_id=0
class Note:
    def __init__(self,memo,tags):
        self.memo = memo
        self.tags = tags        
        self.creation_date=datetime.date.today()
        global last_id
        last_id +=1
        self.id=last_id        

Shell中解释：

n1=Note(‘ddd’)
Traceback (most recent call last):
File “”, line 1, in
NameError: name ‘Note’ is not defined

表示在当前作用域中找不到名为 Xxx 的对象【变量】或函数
实际问题一般是类未定义，Python从模块中导入类的同时就代表在当前模块中找到定义了，所以有可能:
（1）未导入包含对应类声明的模块。
解决：需要在Shell先from notebook import Note
当然，还是产生错误：

from notebook import Note
n1=Note(‘dd’)
Traceback (most recent call last):
File “”, line 1, in
TypeError: init() missing 1 required positional argument: ‘tags’

示例 2：
模块mysubclass.py中代码：

class Contact:
    all_contacts = []
    def __init__(self, name, email):
        self.name = name
        self.email = email
class Supplier(Contact):
    def order(self, order):
        print("If this were a real system we would send ""'{}' order to '{}'".format(order, self.name))

上述代码‘F5’后，在Shell中解释：
1）单独导入子类：from mysubclass import Supplier

from mysubclass import Supplier
s=Supplier(‘’,‘’)
c=Contact(‘’,‘’)
Traceback (most recent call last):
File “”, line 1, in
NameError: name ‘Contact’ is not defined

说明：仅导入子类不能defined父类,
*理论上，如果仅导入父类，必定也不能找到子类的定义
2）解决办法：from mysubclass import Supplier, Contact
或：from mysubclass import *
问题：感觉这种导入办法效率不高。

TypeError:

（1）init() missing 1 required positional argument: ‘tags’

类型错误：init()方法（）内缺少一个位置参数，需要（补全）positional argument: ‘tags’

（2）call_me() takes 1 positional argument but 2 were given

情况：在子类函数中，采用supper()调用父类函数，被调用的函数中保留了参数‘self’，导致的错误
代码：

class BaseClass:
    num_base_calls = 0
    def call_me(self):
        print("Calling method on Base Class")
        self.num_base_calls += 1
class LeftSubclass(BaseClass):
    num_left_calls = 0
    def call_me(self):
        super().call_me(self)
        print("Calling method on Left Subclass")
        self.num_left_calls += 1
class RightSubclass(BaseClass):
    num_right_calls = 0
    def call_me(self):
        BaseClass.call_me(self)
        print("Calling method on Right Subclass")
        self.num_right_calls += 1
class Subclass(LeftSubclass, RightSubclass):
    num_sub_calls = 0
    def call_me(self):
        LeftSubclass.call_me(self)
        RightSubclass.call_me(self)
        print("Calling method on Subclass")
        self.num_sub_calls += 1

正确写法：
1）不采用super()

class LeftSubclass(BaseClass):
    num_left_calls = 0
    def call_me(self):
        BaseClass.call_me(self)   #采用父类名调用时，为啥需要self
        print("Calling method on Left Subclass")
        self.num_left_calls += 1

为啥一定要有self
如果没有，就会出现提示错误：

BaseClass.call_me()
TypeError: call_me() missing 1 required positional argument: ‘self’

2）采用supper()
错误写法：super().call_me(self)
正确写法：super().call_me()
否则就会出现下面的错误提示：

s.call_me()
Traceback (most recent call last):
File “”, line 1, in
File “F:\Traffic Property DeepLearning codes\mytest\multinh.py”, line 21, in call_me
LeftSubclass.call_me(self)
File “F:\Traffic Property DeepLearning codes\mytest\multinh.py”, line 9, in call_me
super().call_me(self)
TypeError: call_me() takes 1 positional argument but 2 were given

（3）TypeError: ‘>’ not supported between instances of ‘builtin_function_or_method’ and ‘int’

示例:

if self.slm.rowCount>0: #判断listview中的model的行数，用到是方法
无把方法当属性用了，即在方法后缺括号（），会提示该错误

（4）TypeError: ‘bool’ object is not callable

示例代码：

```python
elif self.dm.sub_df.empty():

修改为：

```python
```python
elif self.dm.sub_df.empty:  #sub_df是个dataframe

## IndentationError: 
（1）意外缩进 unexpected indent

## 
>>> from multinh import Subclass
>>> s=Subclass()
>>> s.call_me()
Traceback (most recent call last):
  File "", line 1, in 
  File "F:\Traffic Property DeepLearning codes\mytest\multinh.py", line 21, in call_me

    LeftSubclass.call_me(self)
  File "F:\Traffic Property DeepLearning codes\mytest\multinh.py", line 9, in call_me
    super().call_me(self)
TypeError: call_me() takes 1 positional argument but 2 were given

## ValueError: 
### （1）ValueError: The truth value of a DataFrame is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

示例：

```python
elif self.dm.sub_df==None:
            QMessageBox.information(self, "提示", "sub_df不存在，可能需要先“列切”")
        else:
            str=''

问题解析
这个错误是由于在if语句中尝试将Pandas的dataframe转换为bool类型值类判断。因为dataframe可以包含多个值，它们的布尔值不明确。
解决方法：if语句可改为：

elif self.dm.sub_df.empty:

SyntaxError

（1）SyntaxError: unexpected EOF while parsing