Breaking Out of Nested Loops

1. # Special thanks from jinsuun__ on #python irc
2. from dataclasses import dataclass
4. @dataclass
5. class C:
6. m_c: int
7. isLetter : bool = False
8. isNonCharacter : bool = False
9. isNull : bool = False
10. isNumber : bool = False
11. isPrintable : bool = True
12. isSpace : bool = False
13. isUpper : bool = False
14. n = 88
15. c = C(n)
17. match c:
18. case C(0):
19. c.isNull = True
20. case C( m_c = x ) if x in range( 1, 32 ) or x == 127:
21. c.isNonCharacter = True
22. c.isPrintable = False
23. case C(" "):
24. c.isSpace = True
25. case C(x) if x in range( ord("A"), ord("Z") + 1 ):
26. c.isUpper = True
27. c.isLetter = True
28. case C(x) if x in range( ord("a"), ord("z") + 1 ):
29. c.isUpper = False
30. c.isLetter = True
31. case C(x) if x in range( ord("0"), ord("9") + 1 ):
32. c.isNumber = True
33. case _:
34. pass

1. qint8 c(88);
2. bool isLetter (false);
3. bool isNonCharacter(false);
4. bool isNull (false);
5. bool isNumber (false);
6. bool isPrintable (true );
7. bool isSpace (false);
8. bool isUpper (false);
10. switch (c) {
11. default: break;
12. case 0 :
13. isNull = true;
14. [[fallthrough]];
15. case 1 ... 31:
16. case 127 : // Delete
17. isNonCharacter = true;
18. isPrintable = false;
19. break;
21. case ' ':
22. isSpace = true;
23. break;
25. case 'A' ... 'Z':
26. isUpper = true;
27. [[fallthrough]];
28. case 'a' ... 'z':
29. isLetter = true;
30. break;
32. case '0' ... '9':
33. isNumber = true;
34. break;
35. }

Read as:

• if [ expression is true ]
• print x y z
• 'break'out of loop z [ ignore the else ]
• 'break'out of loop y [ ignore the else ]
• 'break'out of loop x.

• if [ expression is true ]
• debug out x y z
• and goto finished [ label ]

Benefits:

• In python, you can place an "else" statement after a loop ( "for" or "while" ) which gets called if the loop exits without a 'break' statement. This is a novell construct absent in c++."

• This code, is clean, and in this particular case, no extra indentation was needed.
• the "goto" label is particularly descriptive: "[ I am finished ] goto finish line."

Drawbacks:

• This "else" feature is esoteric and unknown towards most Python developers.
• The "else" mistakenly seems like the continuation to the "if" statement above.
• This feature does not exist in any other language, making this a non-transferable idiom.
• Indentation structure is bumpy and disorienting.

• None.