Python __len__() Method

The len() Method

The __len__() method controls what the built-in len() function returns for your object.

Example

Return the number of employees in a Company:

class Company:
  def __init__(self, employees):
    self.employees = employees

  def __len__(self):
    return len(self.employees)

c1 = Company(["Emil", "Tobias", "Linus"])

print(len(c1))

Note: Without __len__(), calling len(c1) would raise a TypeError, since Python would not know what "length " means for a Company.