Hello I just have a question about int function. It convert data(for example, string) to int data. My question is how this function works like this? I tried to implement int function myself without any help with built-in function,and I realized this is really hard working. I searched about int function, most of sites have simple description. Just saying 'Return an integer object' like this. It looks easy but hard for me...

I searched and didn't found what I want

Hello I just have a question about int function. It convert data(for example, string) to int data. My question is how this function works like this? I tried to implement int function myself without any help with built-in function,and I realized this is really hard working. I searched about int function, most of sites have simple description. Just saying 'Return an integer object' like this. It looks easy but hard for me...

I searched and didn't found what I want

• python
• integer

• 3 Are you asking how it's possible to parse an int from a string, or are you asking for the source code to Python's built-in int function? – khelwood Commented Feb 6 at 9:45
• 2 If you want to implement your own int() casting (for learning purposes) youcan start implementing the basic case, and progressively add more cases. So instead of an int, start with a function that converts only natural numbers. You can do this by ensuring each character is a digit. Then you can add negative numbers by allowing a - symbol at the beginning. After that you could allow decimals by truncating anything to the right of the decimal point. It really depends what you want your int() function to be able to accept as input. – Cincinnatus Commented Feb 6 at 9:49
• You start as simple as '123' --> 100*1 + 10*2 + 3. Then optimize and generalize to end like this. Yes, coding is hard, good that you realized that. – Jeyekomon Commented Feb 6 at 10:07
• The built-in function is described here: docs.python.org/3/library/functions.html#int – jabaa Commented Feb 6 at 10:15
• Share a small sample code of what you are trying to do for others to understand easily and help you.Thx – SriramN Commented Feb 6 at 10:17

1 Answer 1

Pythons int() function does more than just converting a string to integer.The behavior varies based on the argument and an optional base parameter. we can break down behavior as follows:

1. No arguments int() # returns 0
2. Numeric Arguments
   • If the argument if an integer

      int(5) # return 5
   

   • If argument if a float, then it will remove(truncate) the fractional part

      int(2.04) # return 2
   

3. string Arguments
   • int() strips any whitespace, and also can handle an optional sign(+ or -) and then converts the sequence of digits to an integer.

• For example:

int("  -10  ")  # returns -10

• We can also provide an optional base for conversion

int("1010", 2)  # returns 10 (binaray to decimal)

Steps in the conversion process

1. String Handling
   • Strip whitespace.
   • Handling leading sign(+ or -).
2. Validation
   • To check all charters are vailid digits for the given base.
3. Digit conversion
   • Convert each charater to its corresponding numerical value.
4. Accumulation
   • Compute the integer value by iterating through each digit

For example:

def custom_integer_converter(s, base=10):
    # Ensure input is a string
    if not isinstance(s, str):
        raise TypeError("Input must be a string")
    
    s = s.strip().lower()  # Handle whitespace and case insensitivity
    
    if not s:
        raise ValueError("Empty string after stripping whitespace")
    
    # Determine the sign
    sign = 1
    if s[0] == '-':
        sign = -1
        s = s[1:]
    elif s[0] == '+':
        s = s[1:]
    
    if not s:
        raise ValueError("No digits after sign")
    
    # Validate characters and convert to integer
    value = 0
    for c in s:
        # Convert character to numerical value
        if c.isdigit():
            digit = ord(c) - ord('0')
        else:
            digit = ord(c) - ord('a') + 10
        
        # Check if digit is valid for the base
        if not (0 <= digit < base):
            raise ValueError(f"Invalid character '{c}' for base {base}")
        
        value = value * base + digit
    
    return sign * value

enter image description here The image contains the implementation of the code mentioned above, along with tested inputs.