How to make a class Iterable & create Iterator Class for it ?
Python make class iterable: We are going to see how we can make a class iterable and also creating an iterator class for it.
What’s the need to make a Custom class Iterable ?
User defined classes are not iterable by default. To make the class objects iterable we have to make the class iterable and also create an iterator class for it.
Let’s try to iterate the class with a for loop
class School:
"""
Contains List of Junior and senior school students
"""
def __init__(self):
self._juniorStudents = list()
self._seniorStudents = list()
def addJuniorStudents(self, members):
self._juniorStudents += members
def addSeniorStudents(self, members):
self._seniorStudents += members
def main():
# Create school class object
school = School()
# Add name of junior school students
school.addJuniorStudents(["Seema", "Jenny", "Morris"
])
# Add name of senior school students
school.addSeniorStudents(["Ritika", "Ronnie", "Aaditya"
])
iter(school)
for member in school:
print(member)
# The iter() will throw an error saying school is not iterable
The above code will throw an error as the School class is not iterable yet.
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How to make your Custom Class Iterable | The Iterator Protocol :
In order to make the class iterable, we need to override the iter( ) function inside the class so that the function returns the object of the iterator class which is associated with the iterable class.
class SchoolIterator:
"""Iterator class"""
def __init__(self, school):
# School object reference
self._school = school
# index variable to keep track
self._index = 0
def __next__(self):
"""'Returns the next value from school object's lists"""
if self._index < (
len(self._school._juniorStudents) + len(self._school._seniorStudents)
):
if self._index < len(
self._school._juniorStudents
): # Check if junior student members are fully iterated or not
result = (self._school._juniorStudents[self._index], "junior")
else:
result = (
self._school._seniorStudents[
self._index - len(self._school._juniorStudents)
],
"senior",
)
self._index += 1
return result
# Iteration ends
raise StopIteration
class School:
"""
Contains List of Junior and senior school students
"""
def __init__(self):
self._juniorStudents = list()
self._seniorStudents = list()
def addJuniorStudents(self, members):
self._juniorStudents += members
def addSeniorStudents(self, members):
self._seniorStudents += members
def __iter__(self):
"""Returns Iterator object"""
return SchoolIterator(self)
def main():
# Create school class object
school = School()
# Add name of junior school students
school.addJuniorStudents(["Seema", "Jenny", "Morris"
])
# Add name of senior school students
school.addSeniorStudents(["Ritika", "Ronnie", "Aaditya"
])
iterator = iter(school)
print(iterator)
main()
Output : <__main__.SchoolIterator object at 0x01BC6B10>
The __iter__( ) has been overridden in the School class which now returns the object from the schoolIterator class. And when we call iter( ) function on the school class it will call __iter__( ) function on the object.
How to create an Iterator Class :
In order to create an iterator class, we have to override the __next__( ) function so that every time we call a function, it should return the next iterable class until there are no elements. If there are no next elements, then it should raise the StopIteration.
After that we need to make the class object return the next element from the School class Object’s data member
CODE:
class SchoolIterator:
"""Iterator class"""
def __init__(self, school):
# School object reference
self._school = school
# index variable to keep track
self._index = 0
def __next__(self):
"""'Returns the next value from school object's lists"""
if self._index < (
len(self._school._juniorStudents) + len(self._school._seniorStudents)
):
if self._index < len(
self._school._juniorStudents
): # Check if junior student members are fully iterated or not
result = (self._school._juniorStudents[self._index], "junior")
else:
result = (
self._school._seniorStudents[
self._index - len(self._school._juniorStudents)
],
"senior",
)
self._index += 1
return result
# Iteration ends
raise StopIteration
class School:
"""
Contains List of Junior and senior school students
"""
def __init__(self):
self._juniorStudents = list()
self._seniorStudents = list()
def addJuniorStudents(self, members):
self._juniorStudents += members
def addSeniorStudents(self, members):
self._seniorStudents += members
def __iter__(self):
"""Returns Iterator object"""
return SchoolIterator(self)
def main():
# Create school class object
school = School()
# Add name of junior school students
school.addJuniorStudents(["Seema", "Jenny", "Morris"])
# Add name of senior school students
school.addSeniorStudents(["Ritika", "Ronnie", "Aaditya"])
iterator = iter(school)
print(iterator)
while True:
try:
# Get next element from SchoolIterator object using iterator object
elem = next(iterator)
# Print the element
print(elem)
except StopIteration:
break
main()
Output :
<__main__.SchoolIterator object at 0x01A96B10>
('Seema', 'junior')
('Jenny', 'junior')
('Morris', 'junior')
('Ritika', 'senior')
('Ronnie', 'senior')
('Aaditya', 'senior')
The Working
The iter( ) function calls the overridden __iter__( ) function on the school objects, which would return, the SchoolIterator object. Upon calling the next( ) function, it would call our overridden function __next__( ) internally. The _index variable is being used here to keep track of the iterated elements. So every time we call the function it iterates the objects and in the need it raises the StopIteration.
class SchoolIterator:
"""Iterator class"""
def __init__(self, school):
# School object reference
self._school = school
# index variable to keep track
self._index = 0
def __next__(self):
"""'Returns the next value from school object's lists"""
if self._index < (
len(self._school._juniorStudents) + len(self._school._seniorStudents)
):
if self._index < len(
self._school._juniorStudents
): # Check if junior student members are fully iterated or not
result = (self._school._juniorStudents[self._index], "junior")
else:
result = (
self._school._seniorStudents[
self._index - len(self._school._juniorStudents)
],
"senior",
)
self._index += 1
return result
# Iteration ends
raise StopIteration
class School:
"""
Contains List of Junior and senior school students
"""
def __init__(self):
self._juniorStudents = list()
self._seniorStudents = list()
def addJuniorStudents(self, members):
self._juniorStudents += members
def addSeniorStudents(self, members):
self._seniorStudents += members
def __iter__(self):
"""Returns Iterator object"""
return SchoolIterator(self)
def main():
# Create school class object
school = School()
# Add name of junior school students
school.addJuniorStudents(["Seema", "Jenny", "Morris"])
# Add name of senior school students
school.addSeniorStudents(["Ritika", "Ronnie", "Aaditya"])
iterator = iter(school)
#Using for loop
print(iterator)
for member in school:
print(member)
main()
Output :
<__main__.SchoolIterator object at 0x7fefbe6f34f0>
('Seema', 'junior')
('Jenny', 'junior')
('Morris', 'junior')
('Ritika', 'senior')
('Ronnie', 'senior')
('Aaditya', 'senior')
>