# How to Get the First Digit of an Integer in Python?

In Python, you can get the first digit of an integer in the following ways:

## Using Regular Expression

You can use regular expression in the following way to get the first digit of an integer:

1. Use the `re.search()` method with the `\d` (or `[0-9]`) pattern to get the first digit from numeric string;
2. Convert numeric string back to integer;
3. Add back the minus sign if the number was originally negative.

For example, you can implement this like so:

```import re

def first_digit(num):
# 1: get first digit using regex pattern
match = re.search(r'\d', str(num))
# 2: convert matched item to integer
digit = int(match.group())
# 3: add sign back as needed
return -digit if (num < 0) else digit

print(first_digit(1234)) # 1
print(first_digit(-1234)) # -1
print(first_digit(0)) # 0
print(first_digit(-0)) # 0
```

## Using Floored Division

The following formula would give you the first digit of an integer:

```quotient = floor(abs(integer) / integerLength - 1)
```

You can implement it in the following steps:

1. Convert integer to absolute form;
2. Get length of the integer to determine the divisor;
3. Get the integer part from result of the division;
4. Add back the minus sign if the number was originally negative.
```def first_digit(num):
# 1: convert to absolute form
dividend = abs(num)
# 2: get length of integer and determine divisor
length = len(str(dividend))
divisor = 10 ** (length - 1)
# 3: get integer part from result of division
quotient = dividend // divisor
# 4: add sign back as needed
return -quotient if (num < 0) else quotient

print(first_digit(1234)) # 1
print(first_digit(-1234)) # -1
print(first_digit(0)) # 0
print(first_digit(-0)) # 0
```

Since the dividend is in absolute form, floored division (`//`) works for both, positive and negative, integers.

This works in the following way:

```# num = -1234

# dividend = 1234
# length = 4
# divisor = 10 ^ (4 - 1) = 1000

# quotient = 1234 // 1000
# quotient = 1

# result = -1
```

## Reducing to Single Digit

You can loop over the number and reduce it in each iteration till only a single digit (i.e. digit less than `10`) is left. This can be done in the following steps:

1. Convert integer to absolute form;
2. Reduce number to single digit:
• If integer is greater than `10`, then keep dividing the number by `10` till a number less than `10` is left, or;
• If integer is less than `10`, then return it as is as it's already a single digit number.
3. Get the integer part of the resulting decimal number;
4. Add back the minus sign if the number was originally negative.

For example, you can implement this like so:

```def first_digit(num):
# 1: convert to absolute form
abs_num = abs(num)
# 2: reduce number to single digit
while abs_num >= 10:
abs_num /= 10
# 3: get integer part of decimal number
# 4: add sign back as needed
return int(-abs_num if (num < 0) else abs_num)

print(first_digit(1234)) # 1
print(first_digit(-1234)) # -1
print(first_digit(0)) # 0
print(first_digit(-0)) # 0
```

## Converting to String and Retrieving First Character

You can convert the integer to string and get the first digit in the following steps:

1. Convert integer in absolute form to string;
2. Get the first character;
3. Convert the numeric character back to integer;
4. Add back the minus sign if the number was originally negative.

For example, you can implement this like so:

```def first_digit(num):
# 1: convert absolute form to string
num_str = str(abs(num))
# 2: get first character
first_char = num_str[0]
# 3: convert back to integer
first_digit_unsigned = int(first_char)
# 4: add sign back as needed
return -first_digit_unsigned if (num < 0) else first_digit_unsigned

print(first_digit(1234)) # 1
print(first_digit(-1234)) # -1
print(first_digit(0)) # 0
print(first_digit(-0)) # 0
```

This post was published by Daniyal Hamid. Daniyal currently works as the Head of Engineering in Germany and has 20+ years of experience in software engineering, design and marketing. Please show your love and support by sharing this post.