dict and __dict__

[cls0724]

Here, may i know why when i use

Peter.dict

the following error will occur

Error:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'Celsius' object has no attribute 'dict'

But when i use

Peter.__dict__

It will work. What's the difference? Many thanks.

class Celsius:
    def __init__(self, temperature = 0):
        self.temperature = temperature

    def to_fahrenheit(self):
        return (self.temperature * 1.8) + 32

Peter = Celsius()
Peter.temperature = 37
Peter.__list__