Python Class Methods As Alternative Constructors
The parameters that we have to pass to our constructor would be the class i.e., cls and the string containing the parameters. Moving on towards the working, we have to use a function "split()," that will divide the string into parts. And the parts as results will be stored in a list. We can now pass the parameters to the constructor using the index numbers of the list or by the concept of *args .
split():
It takes a separator as a parameter. If we do not provide any, then the default separator is any whitespace it encounters. Else we can provide any separator to it such as full stop, hash, dash, colon, etc. After separating the string into parts, the split() function stores it into a list in a sequence. For example:
text = "Python tutorial for absolute beginners."
t = text.split()
print(t)Here, we are not providing it any separator as a parameter, so it will automatically divide, taking whitespace as a separator.
The output will be a list, such as:
['Python', 'tutorial', 'for', 'absolute', 'beginners.']Example of Class methods - alternative constructor:
class Date:
def __init__(self, year, month, day):
self.year = year
self.month = month
self.day = day
@classmethod
def from_dash(cls,string):
return cls(*string.split("-"))
date1=Date.from_dash("2008-12-5")
print(date1.year)
#Output: 2008If we want multiple and independent "constructors", we can use class methods. They are usually called factory methods. It does not invoke the default constructor __init__.In the above example, we split the string based on the "-" operator. We first create a class method as a constructor that takes the string and split it based on the specified operator. For this purpose, we use a split() function, which takes the separator as a parameter. This alternative constructor approach is useful when we have to deal with files containing string data separated by a separator.
Example
class Employee:
no_of_leaves = 8
def __init__(self, aname, asalary, arole):
self.name = aname
self.salary = asalary
self.role = arole
def printdetails(self):
return f"The Name is {self.name}. Salary is {self.salary} and role is {self.role}"
@classmethod
def change_leaves(cls, newleaves):
cls.no_of_leaves = newleaves
@classmethod
def from_dash(cls, string):
return cls(*string.split("-"))
harry = Employee("Harry", 255, "Instructor")
rohan = Employee("Rohan", 455, "Student")
karan = Employee.from_dash("Karan-480-Student")
print(karan.no_of_leaves)