In Python, you can convert an integer to a list of digits in the following ways:

- Converting Numeric String to List of Characters;
- Reducing to Single Digit;
- Using Regular Expression.

## Converting Numeric String to List of Characters

If you are certain that the integer is *always* going to be positive, then you can simply do the following:

- Convert integer to numeric string;
- Convert numeric string to a list of characters;
- Use list comprehension to convert each list item to an integer.

For example, this can be implemented like so:

def num_to_list(num): # 1: convert integer to string # 2: convert numeric string to list of chars # 3: convert each numeric string character to integer return [int(char) for char in str(num)] print(num_to_list(12345)) # [1, 2, 3, 4, 5] print(num_to_list(0)) # [0]

However, if the integer can also be negative, then the following are some ways in which you can handle the negative sign (`-`

) when converting an integer to a list of digits:

- Make the Most Significant Digit Negative;
- Add the Minus Sign as a String;
- Add a Leading Digit to Represent the Sign.

### Make the Most Significant Digit Negative:

Making the most significant digit negative means that in the resulting list, if the original number is negative, the first digit will have the negative sign. This means that:

# 12345 becomes [1, 2, 3, 4, 5] # -12345 becomes [-1, 2, 3, 4, 5]

For example, this can be implemented like so:

def num_to_list(num): # 1: convert integer in absolute form to string # 2: convert numeric string to list of chars # 3: convert each numeric string character to integer digits = [int(char) for char in str(abs(num))] # 4: make first digit negative if original number is negative digits[0] = -digits[0] if num < 0 else digits[0] return digits print(num_to_list(12345)) # [1, 2, 3, 4, 5] print(num_to_list(-12345)) # [-1, 2, 3, 4, 5] print(num_to_list(0)) # [0] print(num_to_list(-0)) # [0]

### Add the Minus Sign as a String:

Adding the minus sign (`-`

) as a string means that in the resulting list, if the original number is negative, the first element of the list will have the minus sign as a string:

# 12345 becomes [1, 2, 3, 4, 5] # -12345 becomes ['-', 1, 2, 3, 4, 5]

For example, this can be implemented like so:

def num_to_list(num): # 1: convert integer in absolute form to string # 2: convert numeric string to list of chars # 3: convert each numeric string character to integer digits = [int(char) for char in str(abs(num))] # 4: add minus sign if original number is negative if num < 0: digits.insert(0, '-') return digits print(num_to_list(12345)) # [1, 2, 3, 4, 5] print(num_to_list(-12345)) # ['-', 1, 2, 3, 4, 5] print(num_to_list(0)) # [0] print(num_to_list(-0)) # [0]

### Add a Leading Digit to Represent the Sign

Adding a leading digit to represent the sign means that in the resulting list, the first element can be used to represent the sign (i.e. `0`

for positive integers and `1`

for negative integers):

# 12345 becomes [0, 1, 2, 3, 4, 5] # -12345 becomes [1, 1, 2, 3, 4, 5]

For example, this can be implemented like so:

def num_to_list(num): # 1: convert integer in absolute form to string # 2: convert numeric string to list of chars # 3: convert each numeric string character to integer digits = [int(char) for char in str(abs(num))] # 4: add 0 or 1 as first element in list digits.insert(0, 1 if num < 0 else 0) return digits print(num_to_list(12345)) # [0, 1, 2, 3, 4, 5] print(num_to_list(-12345)) # [1, 1, 2, 3, 4, 5] print(num_to_list(0)) # [0, 0] print(num_to_list(-0)) # [0, 0]

## Reducing to Single Digit

If you are certain that the integer is *always* going to be positive, then you can simply do the following:

- Create a loop;
- Add the last digit (i.e. remainder of
`x % 10`

) as the first element to a new list; - Remove the last digit from the integer in each iteration till there are
*no*digits left.

For example, this can be implemented like so:

def num_to_list(num): digits = [] # 1: create a loop while True: # 2: add last digit as first element in new list digits.insert(0, num % 10) # 3: remove last digit from integer num //= 10 # ...till there are no digits left if num == 0: break return digits print(num_to_list(12345)) # [1, 2, 3, 4, 5] print(num_to_list(0)) # [0]

However, if the integer can also be negative, then you can handle the negative sign (`-`

) in the following ways:

- Make the Most Significant Digit Negative;
- Add the Minus Sign as a String;
- Add a Leading Digit to Represent the Sign.

### Make the Most Significant Digit Negative:

Making the most significant digit negative means that in the resulting list, if the original number is negative, the first digit will have the negative sign. This means that:

# 12345 becomes [1, 2, 3, 4, 5] # -12345 becomes [-1, 2, 3, 4, 5]

For example, this can be implemented like so:

def num_to_list(num): # 1: convert integer to absolute form abs_num = abs(num) digits = [] # 2: create a loop while True: # 3: add last digit as first element in new list digits.insert(0, abs_num % 10) # 4: remove last digit from integer abs_num //= 10 # ...till there are no digits left if abs_num == 0: break # 5: make first digit negative if original number is negative if num < 0: digits[0] = -digits[0] return digits print(num_to_list(12345)) # [1, 2, 3, 4, 5] print(num_to_list(-12345)) # [-1, 2, 3, 4, 5] print(num_to_list(0)) # [0] print(num_to_list(-0)) # [0]

### Add the Minus Sign as a String:

Adding the minus sign (`-`

) as a string means that in the resulting list, if the original number is negative, the first element of the list will have the minus sign as a string:

# 12345 becomes [1, 2, 3, 4, 5] # -12345 becomes ['-', 1, 2, 3, 4, 5]

For example, this can be implemented like so:

def num_to_list(num): # 1: convert integer to absolute form abs_num = abs(num) digits = [] # 2: create a loop while True: # 3: add last digit as first element in new list digits.insert(0, abs_num % 10) # 4: remove last digit from integer abs_num //= 10 # ...till there are no digits left if abs_num == 0: break # 5: add '-' to front of list if num < 0: digits.insert(0, '-') return digits print(num_to_list(12345)) # [1, 2, 3, 4, 5] print(num_to_list(-12345)) # ['-', 1, 2, 3, 4, 5] print(num_to_list(0)) # [0, 0] print(num_to_list(-0)) # [0, 0]

### Add a Leading Digit to Represent the Sign:

Adding a leading digit to represent the sign means that in the resulting list, the first element can be used to represent the sign (i.e. `0`

for positive integers and `1`

for negative integers):

# 12345 becomes [0, 1, 2, 3, 4, 5] # -12345 becomes [1, 1, 2, 3, 4, 5]

For example, this can be implemented like so:

def num_to_list(num): # 1: convert integer to absolute form abs_num = abs(num) digits = [] # 2: create a loop while True: # 3: add last digit as first element in new list digits.insert(0, abs_num % 10) # 4: remove last digit from integer abs_num //= 10 # ...till there are no digits left if abs_num == 0: break # 5: add 0 or 1 as first element in list digits.insert(0, 1 if (num < 0) else 0) return digits print(num_to_list(12345)) # [0, 1, 2, 3, 4, 5] print(num_to_list(-12345)) # [1, 1, 2, 3, 4, 5] print(num_to_list(0)) # [0, 0] print(num_to_list(-0)) # [0, 0]

## Using Regular Expression

If you are certain that the integer is *always* going to be positive, then you can simply do the following:

- Use
`re.findall()`

with a regular expression to convert numeric string to a list of numeric string characters; - Use list comprehension to convert each list item to an integer.

For example, this can be implemented like so:

import re def num_to_list(num): # 1: use regex to match numbers matches = re.findall(r'\d', str(num)) # 2: convert each item to an integer return [int(match) for match in matches] print(num_to_list(12345)) # [1, 2, 3, 4, 5] print(num_to_list(0)) # [0]

However, if the integer can also be negative, then you can handle the negative sign (`-`

) in the following ways:

- Make the Most Significant Digit Negative;
- Add the Minus Sign as a String;
- Add a Leading Digit to Represent the Sign.

### Make the Most Significant Digit Negative:

Making the most significant digit negative means that in the resulting list, if the original number is negative, the first digit will have the negative sign:

# 12345 becomes [1, 2, 3, 4, 5] # -12345 becomes [-1, 2, 3, 4, 5]

For example, this can be implemented like so:

import re def num_to_list(num): # 1: use regex to match numbers matches = re.findall(r'-?\d', str(num)) # 2: convert each item to an integer return [int(match) for match in matches] print(num_to_list(12345)) # [1, 2, 3, 4, 5] print(num_to_list(-12345)) # [-1, 2, 3, 4, 5] print(num_to_list(0)) # [0] print(num_to_list(-0)) # [0]

### Add the Minus Sign as a String:

Adding the minus sign (`-`

) as a string means that in the resulting list, if the original number is negative, the first element of the list will have the minus sign as a string:

# 12345 becomes [1, 2, 3, 4, 5] # -12345 becomes ['-', 1, 2, 3, 4, 5]

For example, this can be implemented like so:

import re def num_to_list(num): # 1: use regex to match numbers matches = re.findall(r'\d', str(num)) # 2: convert each item to an integer digits = [int(match) for match in matches] # 3: add '-' to the front of list if num < 0: digits.insert(0, '-') return digits print(num_to_list(12345)) # [1, 2, 3, 4, 5] print(num_to_list(-12345)) # ['-', 1, 2, 3, 4, 5] print(num_to_list(0)) # [0] print(num_to_list(-0)) # [0]

### Add a Leading Digit to Represent the Sign:

Adding a leading digit to represent the sign means that in the resulting list, the first element can be used to represent the sign (i.e. `0`

for positive integers and `1`

for negative integers):

# 12345 becomes [0, 1, 2, 3, 4, 5] # -12345 becomes [1, 1, 2, 3, 4, 5]

For example, this can be implemented like so:

import re def num_to_list(num): # 1: use regex to match numbers matches = re.findall(r'\d', str(num)) # 2: convert each item to an integer digits = [int(match) for match in matches] # 3: add 0 or 1 as first element in list digits.insert(0, 1 if (num < 0) else 0) return digits print(num_to_list(12345)) # [0, 1, 2, 3, 4, 5] print(num_to_list(-12345)) # [1, 1, 2, 3, 4, 5] print(num_to_list(0)) # [0, 0] print(num_to_list(-0)) # [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.