@@ -433,6 +433,114 @@ isn't exactly like mine but it works just fine it's ok, and you can
433433 >> >
434434 ```
435435
436+
437+ # # More Classes
438+
439+ 1 . Delete all global variables, and use arguments and return values. We also
440+ need to handle the `len (words) == 0 ` case differently, and returning `None `
441+ makes sense now.
442+
443+ ```python
444+ import random
445+
446+
447+ # returns None if the sentence contains 0 words
448+ def change_words_order(sentence):
449+ no_dots_sentence = sentence.replace(' .' ' '
450+ words = no_dots_sentence.split()
451+ if len (words) == 0 :
452+ return None
453+
454+ lowercase_words = []
455+ for word in words:
456+ lowercase_words.append(word.lower())
457+ random.shuffle(lowercase_words)
458+
459+ # in lowercase_words[0], first character uppercase, rest lowercase
460+ # note that empty_list_or_empty_string[0] doesn't work
461+ # lowercase_words is not empty because len(words) == 0 was handled separately
462+ # lowercase_words[0] is not empty because it came from .split()
463+ lowercase_words[0 ] = lowercase_words[0 ][0 ].upper() + lowercase_words[0 ][1 :]
464+ return ' ' + ' .'
465+
466+
467+ def main():
468+ print (" This program changes the order of the words of a sentence randomly."
469+ print ()
470+
471+ while True :
472+ sentence = input (' Enter a sentence: '
473+ new_sentence = change_words_order(sentence)
474+ if new_sentence is not None :
475+ print (new_sentence)
476+
477+ if __name__ == ' __main__'
478+ main()
479+ ```
480+
481+ 2 . This answer doesn' t contain any code because I haven'
482+ program, and I don' t know what your program does. You can
483+ [show your program to me](../ contact- me.md) if you want to.
484+
485+ If your program is short, the cleaned program that uses arguments and
486+ return values is probably cleaner.
487+
488+ 3 . See 2 .
489+
490+ 4 . One way is to replace all the allowed characters with empty strings (delete
491+ them), and see what is left. Of course, add `import string` to the beginning
492+ of the program.
493+
494+ ```python
495+ bad_characters = user_name
496+ for good_character in (string.ascii_letters + string.digits + ' -'
497+ bad_characters = bad_characters.replace(good_character, ' '
498+
499+ if bad_characters != ' '
500+ return " Username must not contain these characters: " + bad_characters
501+ ```
502+
503+ For phone numbers, you need to decide how they have to be entered. The code
504+ below accepts `xxx- xxx- xxxx` , where each `x` means a digit. The code ended
505+ up being quite long , so I put it to a separate function.
506+
507+ I' m assuming that all phone numbers are 10 digits long. This is probably
508+ wrong, and in a real program you should instead figure out what' s the
509+ correct way to validate a phone number, or find someone else ' s code that
510+ does it correctly and use that.
511+
512+ ```python
513+ def validate_phone_number(phone_number):
514+ # split 'xxx-yyy-zzzz' to ['xxx', 'yyy', 'zzzz']
515+ parts = phone_number.split(' -'
516+ if len (parts) != 3 :
517+ return False
518+ if len (parts[0 ]) != 3 or len (parts[1 ]) != 3 or len (parts[2 ]) != 4 :
519+ return False
520+
521+ for part in parts:
522+ for character in part:
523+ if character not in string.digits:
524+ return False
525+
526+ return True
527+ ```
528+
529+ Now you can use this function like this:
530+
531+ ```python
532+ if not validate_phone_number(self .work_phone_number):
533+ return " work phone number must be entered as xxx-xxx-xxxx"
534+ if not validate_phone_number(self .personal_phone_number):
535+ return " personal phone number must be entered as xxx-xxx-xxxx"
536+ ```
537+
538+ It' s also important to tell the user how to enter the phone numbers.
539+ For example, you can replace `input (" Work phone number: " with
540+ `input (" Work phone number (xxx-xxx-xxxx, each x is a digit): " or
541+ something like that.
542+
543+
436544** *
437545
438546If you have trouble with this tutorial please [tell me about
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