19 Python 3

发布时间：2023-04-15 14:11:21 所属栏目：教程来源：

导读：Creating Instance Objects
To create instances of a class, you call the class using class name and pass in whatever arguments its __init__ method accepts.

This would create first object of Employee

Creating Instance Objects
To create instances of a class, you call the class using class name and pass in whatever arguments its __init__ method accepts.

This would create first object of Employee class
emp1 = Employee("Zara", 2000)
This would create second object of Employee class
emp2 = Employee("Manni", 5000)
Accessing Attributes
You access the object's attributes using the dot operator with object. Class variable would be accessed using class name as follows −

emp1.displayEmployee()
emp2.displayEmployee()
print ("Total Employee %d" % Employee.empCount)
Now, putting all the concepts together −

Live Demo
#!/usr/bin/python3

class Employee:
'Common base class for all employees'
empCount = 0

def __init__(self, name, salary):
self.name = name
self.salary = salary
Employee.empCount += 1

def displayCount(self):
print ("Total Employee %d" % Employee.empCount)

def displayEmployee(self):
print ("Name : ", self.name, ", Salary: ", self.salary)

#This would create first object of Employee class"
emp1 = Employee("Zara", 2000)
#This would create second object of Employee class"
emp2 = Employee("Manni", 5000)
emp1.displayEmployee()
emp2.displayEmployee()
print ("Total Employee %d" % Employee.empCount)
When the above code is executed, it produces the following result −

Name : Zara ,Salary: 2000
Name : Manni ,Salary: 5000
Total Employee 2
You can add, remove, or modify attributes of classes and objects at any time −

emp1.salary = 7000 # Add an 'salary' attribute.
emp1.name = 'xyz' # Modify 'age' attribute.
del emp1.salary # Delete 'age' attribute.
Instead of using the normal statements to access attributes, you can use the following functions −

The getattr(obj, name[, default]) − to access the attribute of object.

The hasattr(obj,name) − to check if an attribute exists or not.

The setattr(obj,name,value) − to set an attribute. If attribute does not exist, then it would be created.

The delattr(obj, name) − to delete an attribute.

hasattr(emp1, 'salary') # Returns true if 'salary' attribute exists
getattr(emp1, 'salary') # Returns value of 'salary' attribute
setattr(emp1, 'salary', 7000) # Set attribute 'salary' at 7000
delattr(emp1, 'salary') # Delete attribute 'salary'
Built-In Class Attributes
Every Python class keeps following built-in attributes and they can be accessed using dot operator like any other attribute −

__dict__ − Dictionary containing the class's namespace.

__doc__ − Class documentation string or none, if undefined.

__name__ − Class name.

__module__ − Module name in which the class is defined. This attribute is "__main__" in interactive mode.

__bases__ − A possibly empty tuple containing the base classes, in the order of their occurrence in the base class list.

For the above class let us try to access all these attributes −

Live Demo
#!/usr/bin/python3

class Employee:
'Common base class for all employees'
empCount = 0

def __init__(self, name, salary):
self.name = name
self.salary = salary
Employee.empCount += 1

def displayCount(self):
print ("Total Employee %d" % Employee.empCount)

def displayEmployee(self):
print ("Name : ", self.name, ", Salary: ", self.salary)

emp1 = Employee("Zara", 2000)
emp2 = Employee("Manni", 5000)
print ("Employee.__doc__:", Employee.__doc__)
print ("Employee.__name__:", Employee.__name__)
print ("Employee.__module__:", Employee.__module__)
print ("Employee.__bases__:", Employee.__bases__)
print ("Employee.__dict__:", Employee.__dict__ )
When the above code is executed, it produces the following result −

Employee.__doc__: Common base class for all employees
Employee.__name__: Employee
Employee.__module__: __main__
Employee.__bases__: (<class 'object'>,)
Employee.__dict__: {
'displayCount': <function Employee.displayCount at 0x0160D2B8>,
'__module__': '__main__', '__doc__': 'Common base class for all employees',
'empCount': 2, '__init__':
<function Employee.__init__ at 0x0124F810>, 'displayEmployee':
<function Employee.displayEmployee at 0x0160D300>,
'__weakref__':
<attribute '__weakref__' of 'Employee' objects>, '__dict__':
<attribute '__dict__' of 'Employee' objects>
}

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