The easiest and most efficient way to convert a string to an integer in Python is to use the “int()” function. It accepts a valid string integer literal as an argument and returns an integer. For example, int(“456”) would return 456.

Python string is a sequence of characters, and an integer is a numeric value. You cannot perform arithmetic operations on a string; for that, you must convert the string representation to a numeric value.

For example, if you use the input() function to get the input from a user, its value is always a string. To perform summation, you must convert that string value to an integer value.

Basic conversion

Define a valid string that is an integer literal:

string_value = "1921" 

print(string_value)
# Output: "1921"

print(type(string_value))
# Output: <class 'str'>

integer_value = int(string_value)

print(integer_value) 
# Output: 1921

print(type(integer_value))
# Output: <class 'int'>

You can also use the string.isdigit() method before conversion to check whether all characters in a string are digits. If all characters are digits, the method returns True. After that, you can use the int() function for the conversion.

def convert_to_integer(value: str):
    """Converts a string to an integer if it represents a valid number."""
    if value.isdigit():
        integer_value = int(value)
        print(f"Converted Value: {integer_value}")
        print(f"Type: {type(integer_value)}")
    else:
        print(f"Error: '{value}' is not a valid integer.")


# Example usage
string_value = "101"
convert_to_integer(string_value)

# Output:
# Converted Value: 101
# Type: <class 'int'>

Handling Signs

In practical applications, the string contains a positive (+) or negative (-) sign. During conversion, those signs are handled automatically. It won’t throw any errors.

string_value = "-1921" 

print(string_value)
# Output: "-1921"

print(type(string_value))
# Output: <class 'str'>

integer_value = int(string_value)

print(integer_value) 
# Output: -1921

print(type(integer_value))
# Output: <class 'int'>

Whitespace

If a valid integer string contains whitespace, the int() function ignores it and returns the normal integer output.

str_int = "  45  "

num = int(str_int)

print(num)
# Output: 45

print(type(num))
# Output: <class 'int'>

Empty Strings

Your input string maybe empty. So, check before conversion.

str = ""

if str.strip():
    num = int(str)

Leading Zeros

If your string contains 0s at the start of the string, you can strip it using the lstrip() function.

data_str = "00123"

print(data_str)
# Output: 00123

print(type(data_str))
# Output: <class 'str'>

main_str = data_str.lstrip("0")
num = int(main_str)

print(num)
# Output: 123

print(type(num))
# Output: <class 'int'>

Specifying a Base (Binary, Octal, Hexadecimal)

What if a string is in a different base? The int() function accepts the “base” as a second argument.

So, you can use the “base” argument to convert that string into an appropriate integer. Like hexadecimal or binary. Ensure that the string is suitable for the specified base.

For example, int(“1a”, 16) would convert the hexadecimal “1a” to 26 in decimal.

Binary string

num = int("1010", 2)

print(num)
# Output: 10

print(type(num))
# Output: <class 'int'>

Octal string

num = int("12", 8)

print(num)
# Output: 10

print(type(num))
# Output: <class 'int'>

Hex string

num = int("A", 16)

print(num)
# Output: 10

print(type(num))
# Output: <class 'int'>

Auto-Detect Base

Use base=0 to infer from prefixes (0b, 0o, 0x):

num = int("0b1010", 0)

print(num)
# Output: 10
print(type(num))
# Output: <class 'int'>

num_2 = int("0x1A", 0)
print(num_2)
# Output: 26
print(type(num_2))
# Output: <class 'int'>

Preprocessing Strings

Remove Commas/Currency Symbols

If a string contains a valid integer but also has symbols or commas, we can replace it with an empty string using the replace() method and then convert the string into an integer.

price = "$1,234"

print(price)
# Output: $1,234

print(type(price))
# Output: <class 'str'>

num = int(price.replace("$", "").replace(",", ""))

print(num)
# Output: 1234

print(type(num))
# Output: <class 'int'>

Scientific Notation

If your input string contains scientific letters like “e“, you can use the float() function to normalize the value and then apply the int() function to it.

data_str = "1.23e4"

print(data_str)
# Output: 1.23e4

print(type(data_str))
# Output: <class 'str'>

num = int(float(data_str))

print(num)
# Output: 12300

print(type(num))
# Output: <class 'int'>

Locale-Specific Parsing

Python provides a “locale” module that you can use to set the locale for your current program and then convert it.

import locale
locale.setlocale(locale.LC_ALL, 'en_US.UTF-8')

data_str = "5,678"

print(data_str)
# Output: 1.23e4

print(type(data_str))
# Output: <class 'str'>

num = int(locale.atoi(data_str))

print(num)
# Output: 5678

print(type(num))
# Output: <class 'int'>

Converting from Float Strings

If you are dealing with a string representing floating-point numbers, you can truncate decimal values or round them before converting them into an integer.

Truncate Decimal Values

float_str = "123.45"

print(float_str)
# Output: 123.45

print(type(float_str))
# Output: <class 'str'>

num = int(float(float_str))

print(num)
# Output: 123.45

print(type(num))
# Output: <class 'int'>

Rounding First

float_str = "123.6"

print(float_str)
# Output: 123.6

print(type(float_str))
# Output: <class 'str'>

num = int(round(float("123.6")))

print(num)
# Output: 124

print(type(num))
# Output: <class 'int'>

Here are two alternate ways to convert a string to an integer for your knowledge:

Alternate approach 1: Using ast.literal_eval()

The ast.literal_eval() function accepts a string and returns an integer. It is helpful when you parse the data from untrusted sources or when you need to ensure that only safe literals are evaluated from a string.

from ast import literal_eval

string_value = "101"

print(string_value)
# Output: "101"

print(type(string_value))
# Output: <class 'str'>

integer_value = literal_eval(string_value)

print(integer_value)
# Output: 101

print(type(integer_value))
# Output: <class 'int'>

Alternate approach 2: Using eval()

The eval() method is not recommended due to security risks if the input is not sanitized, as it can execute arbitrary code. It accepts a string as an argument and returns an integer representation.

string_value = "101"

print(string_value)
# Output: "101"

print(type(string_value))
# Output: <class 'str'>

integer_value = eval(string_value)

print(integer_value)
# Output: 101

print(type(integer_value))
# Output: <class 'int'>

That’s all!