Scenario

A text file contains a list of phone numbers in various formats. You need to validate each phone number against specific format requirements and mark them accordingly.

Task

Write a Python script at /home/interview/validate_phones.py that reads /home/interview/phone_numbers.txt, validates each phone number using regex to match the formats (XXX) XXX-XXXX or XXX-XXX-XXXX, and writes the results to /home/interview/validation_results.txt with each number marked as VALID or INVALID.

Example

Expected output format in /home/interview/validation_results.txt:

(555) 123-4567 - VALID
555-123-4567 - VALID
555.123.4567 - INVALID
5551234567 - INVALID

Step 1: Examine the input file

head -20 /home/interview/phone_numbers.txt

Review the different phone number formats present in the dataset.

Step 2: Create the validation script

nano /home/interview/validate_phones.py

Write a script that validates phone numbers using regex:

import re

# Regex patterns for valid formats
# (XXX) XXX-XXXX or XXX-XXX-XXXX
pattern = r'^(\(\d{3}\) \d{3}-\d{4}|\d{3}-\d{3}-\d{4})$'

# Read phone numbers
with open('/home/interview/phone_numbers.txt', 'r') as f:
    phone_numbers = f.readlines()

# Validate and mark each number
results = []
valid_count = 0
invalid_count = 0

for phone in phone_numbers:
    phone = phone.strip()
    if re.match(pattern, phone):
        results.append(f"{phone} - VALID")
        valid_count += 1
    else:
        results.append(f"{phone} - INVALID")
        invalid_count += 1

# Write results
with open('/home/interview/validation_results.txt', 'w') as f:
    f.write('\n'.join(results))

print(f"Validated {len(phone_numbers)} phone numbers")
print(f"Valid: {valid_count}, Invalid: {invalid_count}")

The regex uses alternation | to match either format and anchors ^$ to ensure the entire string matches.

Step 3: Run the script

python3 /home/interview/validate_phones.py

Step 4: Verify the output

head -20 /home/interview/validation_results.txt

Each phone number should be marked as VALID or INVALID based on format matching.