Exercise 12-03:
Using the pattern_check function, write a function that detects a date in the format dd/mm/yy where dd is the day, mm the month, and yy the year. The function should only detect the date pattern and it does not need to verify whether the date is valid.
Answer:
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# Python From Scratch
# Author: Nilo Ney Coutinho Menezes
# Editora Novatec (c) 2010-2025 - LogiKraft 2025
# Site: https://pythonfromscratch.com
# ISBN: 978-85-7522-949-1 (Paperback), 978-85-7522-950-7 (hardcover), 978-85-7522-951-4 (ebook)
#
# File: chapter 12/exercise-12-03.py.py
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# Functions number, sequence and check pattern from listing 12.5
from functools import partial
def number(input_string, min_qty, max_qty):
num = 0
for character in input_string:
if character.isnumeric():
num += 1
else:
break
if min_qty <= num <= max_qty:
return num, 0, num - 1
else:
return -1, -1, -1
def sequence(input_string, pattern):
position, max_position = 0, len(pattern)
for character in input_string:
if character == pattern[position]:
position += 1 # Same characters, test next character
else:
break # Out of sequence
if position == max_position: # Found entire sequence
return 1, 0, position - 1
return -1, -1, -1
def check_pattern(input_string, patterns):
position = 0
for pattern in patterns:
found, _, end = pattern(input_string[position:])
if found > 0:
position += end + 1
else:
return -1, -1, -1
return 1, 0, position - 1
two_numbers = partial(number, min_qty=2, max_qty=2)
slash = partial(sequence, pattern="/")
pattern = [two_numbers, slash, two_numbers, slash, two_numbers]
# Here's a small list of inputs to facilitate visualization
inputs = [
"12/03/24", # Pattern found
"12/3/2024", # Pattern not found
"Twelfth of March 12/03", # Pattern not found
"12-03-24 12/03/2024 abc 21/30/24", # Pattern found
"12/03/24 12/03/624 abc 21/30/24", # Pattern found twice
]
for input_string in inputs:
print("Input:", input_string)
found = False
position = 0
while position < len(input_string):
found, start, end = check_pattern(input_string[position:], pattern)
if found > 0:
print(f"Date positions: {position+start} to {position+end} ", end="")
print("Date:", input_string[position + start : position + end + 1])
found = True
position += end + 1
else:
position += 1
if not found:
print("No date found in input")
print()