Simple example to explain name mangling in python.

name_mangling.py

# coding: utf-8


class Image(object):
  
  def __format(self):
    return 'PNG'
  

image = Image()

try:
  image.__format() # will raise AttributeError
except AttributeError as exc:
  print(exc)

print(dir(image)) # but the format method exists with another name

format_ = getattr(image, '_Image__format')()
print(format_) # PNG