Why does assigning to True/False not work as I expect?

by

Python has these two (among others) builtin objects. They are just objects; in the beginning, they don’t have any names yet, but to know what we refer to, let’s call them 0x600D and 0xBAD.

Before starting to execute a Python (2.x) script, the name True gets bound to the object 0x600D, and the name False gets bound to the object 0xBAD, so when the program refers to True, it looks at 0x600D.

Because 0x600D and 0xBAD know that they are usually used by the names True and False, that’s what they output when they get printed, i.e. the __str__ method of 0x600D returns 'True' and so on.

True = False

now binds the name True to a different object. From now on, both names True and False refer to the same object 0xBAD, which, when printed, outputs False.

True = True

doesn’t really do anything: It takes the object referred to by the name True, and binds the new (and old) name True to this object. Since (because of the previous step) True refers to 0xBAD before this, it still refers to 0xBAD after this. Hence, printing still outputs False.

True = not True

first takes the object that the name True is bound to, which is 0xBAD. It gives this object to the not operator. not doesn’t care (or know) what name is used here to refer to 0xBAD, it just knows that when given 0xBAD it should return 0x600D. This return value is then given to the assignment operator =, binding the name True to this object.

Since the name True now once more refers to the object 0x600D, calling print True outputs True, and the world is good again.

More Related Contents:

  1. What exactly do “u” and “r” string flags do, and what are raw string literals?
  2. How can I force division to be floating point? Division keeps rounding down to 0?
  3. Why does the division get rounded to an integer?
  4. How can I concatenate str and int objects?
  5. Setting the correct encoding when piping stdout in Python
  6. How can I read large text files line by line, without loading it into memory?
  7. How do I keep Python print from adding newlines or spaces? [duplicate]
  8. How to get string objects instead of Unicode from JSON?
  9. No module named MySQLdb
  10. How to pretty-print a numpy.array without scientific notation and with given precision?
  11. f-strings giving SyntaxError?
  12. Python unexpected EOF while parsing
  13. How to print variables without spaces between values [duplicate]
  14. Why does Python print unicode characters when the default encoding is ASCII?
  15. Why can’t I use the method __cmp__ in Python 3 as for Python 2?
  16. What is the difference between encode/decode?
  17. Python 2 CSV writer produces wrong line terminator on Windows
  18. How can I get 2.x-like sorting behaviour in Python 3.x?
  19. Printing without newline (print ‘a’,) prints a space, how to remove?
  20. What does “ mean in Python?
  21. Why does input() give a SyntaxError when I just press enter?
  22. Convert float to string in positional format (without scientific notation and false precision)
  23. compare lines in a file with a string
  24. UnicodeDecodeError: ‘utf8’ codec can’t decode bytes in position 3-6: invalid data
  25. Replace list of list with “condensed” list of list while maintaining order
  26. What is more ‘pythonic’ for ‘not’ [duplicate]
  27. Printing a string prints ‘u’ before the string in Python?
  28. How do implicit relative imports work in Python?
  29. What arguments does Python sort() function have?
  30. Swapping uppercase and lowercase in a string [duplicate]

Leave a Comment