Normalization converts varied input into a consistent form before further processing. For word counts, case and punctuation matter: `This`, `this.`, and `this,` would otherwise be counted separately. For phone numbers, different separators can be replaced with one output format. section 21.2.2 section 16.6.2
Choose the rules for the data and the task:
- For text, make letters one case, remove punctuation, then split into words. Processing a file line by line can save memory. section 6.10
- For phone numbers, extract digits, check length and required area-code and exchange digits, add a missing country code, then insert separators. section 16.6.2
Preparing words for a count
`words = paragraph.lower().replace('.', '').replace(',', '').split()` makes case consistent and removes two punctuation marks before splitting. It does not remove every mark: a token such as `reefs--commerce` can remain joined. For more punctuation characters, `str.translate()` can replace them in one operation. section 21.2.2
import re
def normalize_phone_number(phone_number):
phone_number = re.sub(r'\D', '', phone_number) #1
if len(phone_number) not in [10, 11]: #2
raise ValueError("Invalid phone number length")
if not re.match(r'^[2-9][0-8][0-9][2-9]',
phone_number[-10:]): #3
raise ValueError("Invalid area code or exchange code")
if len(phone_number) == 10: #4
phone_number = '1' + phone_number
phone_number = re.sub(r'(\d{1})(\d{3})(\d{3})(\d{4})',
r'\1-\2-\3-\4', phone_number) #5
return phone_number
# Test the function.
phone_numbers = ["+1 223-456-7890",
"1-223-456-7890",
"+1 223 456-7890",
"(223) 456-7890",
"1 223 456 7890",
"999.456.7890",
"1-989-111-2222",
"223.456.7890"]
for number in test_numbers:
try:
normalized_phone_number = normalize_phone_number(number)
print(f'{normalized_phone_number}')
except ValueError as e:
print(f'{number} is not a valid phone number: {e}')
1-223-456-7890
1-223-456-7890
1-223-456-7890
1-223-456-7890
1-223-456-7890
999.456.7890 is invalid: Invalid area code or exchange code
1-989-111-2222 is invalid: Invalid area code or exchange code
1-223-456-7890
#1 Removes all nondigit (\D) characters
#2 The length must be 10 or 11.
#3 Checks area code and exchange at once
#4 Adds country code if needed
#5 Adds dashes between elements
The phone-number function uses `re.sub(r'\D', '', phone_number)` to discard nondigits, validates the remaining digits, adds `1` when needed, and formats the result with hyphens. Stripping separators is simpler when the input is already known to be a phone number; it is not a substitute for deciding which inputs are acceptable. section 16.6.2
