Get the first or first N digits of a Number in Python

# Table of Contents

1. Get the first digit of a number in Python
2. Get the first N digits of a number in Python
3. Get only the first Number in a String in Python
4. Find the index of the first Digit in a String in Python

# Get the first digit of a number in Python

To get the first digit of a number:

1. Use the str() class to convert the number to a string.
2. Access the character at index 0.
3. Use the int() class to convert the result to an integer.

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num = 246810

first = int(str(num)[0])

print(first)  # 👉️ 2

If you need to get the first N digits of a number, click on the following subheading:

• Get the first N digits of a number in Python

We used the str() class to convert the integer to a string so we can access the string at a specific index.

The next step is to access the character at index 0 to get the first digit of the number.

Once we have the first digit, we can use the int() class to convert the string to an integer.

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num = 246810

first = int(str(num)[0])

print(first)  # 👉️ 2

You can use the same approach if you need to get the first N digits of a number.

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num = 246810

first2 = int(str(num)[:2])
print(first2)  # 👉️ 24

first3 = int(str(num)[:3])
print(first3)  # 👉️ 246

The syntax for string slicing is my_str[start:stop:step].

The slice my_str[:2] starts at index 0 and goes up to, but not including index 2.

# Get the first digit of a number using recursion

Alternatively, you can use recursion.

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def get_first_digit(number):
    if number < 10:
        return number
    return get_first_digit(number // 10)


print(get_first_digit(2468))  # 👉️ 2
print(get_first_digit(514))  # 👉️ 5
print(get_first_digit(14))  # 👉️ 1
print(get_first_digit(8))  # 👉️ 8

The function checks if the number is less than 10 and if the condition is met, it returns the number.

Otherwise, it returns the result of calling itself with the number floor-divided by 10.

Division / of integers yields a float, while floor division // of integers results in an integer.

The result of using the floor division operator is that of a mathematical division with the floor() function applied to the result.

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my_num = 50

print(my_num / 5)  # 👉️ 10.0 (float)
print(my_num // 5)  # 👉️ 10 (int)

We divide the number by 10 until we get a single-digit number and return the result.

# Get the first N digits of a number in Python

To get the first N digits of a number:

1. Use the str() class to convert the number to a string.
2. Use string slicing to select the first N characters of the string.
3. Use the int() class to convert the result to an integer.

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number = 13579

# ✅ Get the first 2 digits of a number
first_2 = int(str(number)[:2])
print(first_2)  # 👉️ 13

# ✅ Get the first 3 digits of a number
first_3 = int(str(number)[:3])
print(first_3)  # 👉️ 135

We used the str() class to convert the integer to a string so we can use string slicing.

The first example returns the first two digits of the number.

The slice my_str[:2] starts at index 0 and goes up to, but not including index 2.

The syntax for string slicing is my_str[start:stop:step].

The start index is inclusive, whereas the stop index is exclusive (up to, but not including).

Once we have the first 2 digits, we use the int() class to convert the string to an integer.

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number = 13579

first_2 = int(str(number)[:2])
print(first_2)  # 👉️ 13

# Get the first N digits of a number using recursion

Alternatively, you can use recursion.

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def get_first_two_digits(number):
    if number < 100:
        return number
    return get_first_two_digits(number // 10)


print(get_first_two_digits(2468))  # 👉️ 24
print(get_first_two_digits(514))  # 👉️ 51
print(get_first_two_digits(95))  # 👉️ 95
print(get_first_two_digits(7))  # 👉️ 7

The function checks if the number is less than 100 and if the condition is met, it returns the number.

Otherwise, it returns the result of calling itself with the number floor-divided by 10.

The result of using the floor division operator is that of a mathematical division with the floor() function applied to the result.

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my_num = 50

print(my_num / 5)  # 👉️ 10.0 (float)
print(my_num // 5)  # 👉️ 10 (int)

We divide the number by 10 until we get a 2-digit number and return the result.

If you need to get the first three digits of the number, you would check if the number is less than 1000.

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def get_first_three_digits(number):
    if number < 1000:
        return number
    return get_first_three_digits(number // 10)


print(get_first_three_digits(2468))  # 👉️ 246
print(get_first_three_digits(51410))  # 👉️ 514
print(get_first_three_digits(95799))  # 👉️ 957
print(get_first_three_digits(719292))  # 👉️ 719

# Get only the first Number in a String in Python

If you need to get only the first number in a string, use re.search().

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import re

my_str = 'bobby12hadz34.com'


match = re.search(r'\d+', my_str)

if match:
    # 👇️ First number found: 12
    print('First number found:', match.group())

    # 👇️ Index of first digit: 5
    print('Index of first digit:', match.start())
else:
    print('The string does NOT contain any numbers')

The re.search() method looks for the first location in the string where the provided regular expression produces a match.

The first argument we passed to the re.search() method is a regular expression.

The \d character matches the digits [0-9] (and many other digit characters).

The + matches the preceding character (a digit) 1 or more times.

You can use the start() method on the match object to get the index of the first digit in the string.

If you ever need help reading or writing a regular expression, consult the regular expression syntax subheading in the official docs.

The page contains a list of all of the special characters with many useful examples.

We used the match.group() method to get the entire match.

You can also use a range of digits [0-9] if you find the regular expression more readable.

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import re

my_str = 'bobby12hadz34.com'


match = re.search(r'[0-9]+', my_str)

if match:
    # 👇️ First number found: 12
    print('First number found:', match.group())
else:
    print('The string does NOT contain any numbers')

The square brackets [] are used to indicate a set of characters.

The 0-9 characters match the digits in the range.

# Find the index of the first Digit in a String in Python

To find the index of the first digit in a string:

1. Use a for loop to iterate over the string with enumerate().
2. Use the str.isdigit() method to check if each character is a digit.
3. Once the index is found, use the break statement to break out of the loop.

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my_str = 'bobby123hadz'

for index, char in enumerate(my_str):
    if char.isdigit():
        print(index, char)  # 👉️ 5, 1
        break

We used the enumerate() function to get access to the index of the current iteration.

The enumerate() function takes an iterable and returns an enumerate object containing tuples where the first element is the index and the second is the corresponding item.

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my_str = 'bobby'

for index, char in enumerate(my_str):
    print(char, index)  # 👉️ b 0, o 1, b 2, b 3, y 4

The str.isdigit() method returns True if all characters in the string are digits and there is at least 1 character, otherwise False is returned.

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print('A'.isdigit()) # 👉️ False
print('5'.isdigit()) # 👉️ True

Once we find a digit, we use the break statement to break out of the loop.

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my_str = 'bobby123hadz'

for index, char in enumerate(my_str):
    if char.isdigit():
        print(index, char)  # 👉️ 5, 1
        break

The break statement breaks out of the innermost enclosing for or while loop.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• Get the last or last N digits of a Number in Python
• Count the decimal places of a Float in Python
• Get the first character of each string in a List in Python
• Get the length of an Integer or a Float in Python