Mobile Number Verify

Source: Dev.to

Overview

A simple Python function that validates Indian mobile numbers based on allowed characters and specific digit rules.

Validation Rules

Condition 1 – Allowed characters

Only digits (0‑9), the plus sign (+), or a space ( ) are permitted. Any other character causes the function to reject the input.

Condition 2 – 10‑digit numbers

If the input length is 10, the first digit must be between 6 and 9 (inclusive).

Condition 3 – Numbers with country code +91 (no space)

If the input length is 13, it must start with +91. The fourth digit (index 3) must be between 6 and 9.

Condition 4 – Numbers with country code +91 followed by a space

If the input length is 14, it must start with +91 (including the trailing space). The fifth digit (index 4) must be between 6 and 9.

Function Implementation (Python)

def mobile(n):
    # Condition 1 – allowed characters
    i = 0
    while i < len(n):
        if ("0" <= n[i] <= "9") or n[i] == "+" or n[i] == " ":
            i += 1
        else:
            return "characters and special characters not allowed"

    # Condition 2 – 10‑digit format
    if len(n) == 10:
        if "6" <= n[0] <= "9":
            return "valid"
        return "First number should not be less than 6"

    # Condition 3 – +91 format (no space)
    if len(n) == 13:
        if n[:3] == "+91":
            if "6" <= n[3] <= "9":
                return "valid"
            return "Fourth number should not be less than 6"
        return "First three numbers should be +91"

    # Condition 4 – +91 format with trailing space
    if len(n) == 14:
        if n[:4] == "+91 ":
            if "6" <= n[4] <= "9":
                return "valid"
            return "Fifth number should not be less than 6"
        return "First four numbers should be +91 "

    return "Please enter a valid mobile number"

Usage

print(mobile(input("Enter your mobile number: ")))