Python Program for Remove leading zeros from a Number given as a string
Last Updated :
18 Apr, 2025
Given numeric string str, the task is to remove all the leading zeros from a given string. If the string contains only zeros, then print a single "0".
Examples:
Input: str = "0001234"
Output: 1234
Explanation:
Removal of leading substring "000" modifies the string to "1234".
Hence, the final answer is "1234".
Input: str = "00000000"
Output: 0
Explanation:
There are no numbers except 0
Remove leading zeros from a Number given
The simplest approach to solve the problem is to traverse the string up to the first non-zero character present in the string and store the remaining string starting from that index as the answer. If the entire string is traversed, it means all the characters in the string are '0'. For this case, store "0" as the answer. Print the final answer.
Below is the implementation of the above idea:
Python
# Python Program to remove all the leading
# zeros from a given numeric string
# Function to remove the leading zeros
def removeLeadingZeros(num):
# traverse the entire string
for i in range(len(num)):
# check for the first non-zero character
if num[i] != '0':
# return the remaining string
res = num[i::];
return res;
# If the entire string is traversed
# that means it didn't have a single
# non-zero character, hence return "0"
return "0";
# Driver Code
num = "1023";
print(removeLeadingZeros(num));
num = "00123";
print(removeLeadingZeros(num));
Output
1023
123
Time Complexity: O(N)
Auxiliary Space: O(N)
Remove leading zeros from a Number given Using Space-Efficient Approach
Follow the steps below to solve the problem in constant space using Regular Expression:
- Create a Regular Expression as given below to remove the leading zeros
regex = "^0+(?!$)"
where:
^0+ match one or more zeros from the beginning of the string.
(?!$) is a negative look-ahead expression, where "$" means the end of the string.
- Use the inbuilt replaceAll() method of the String class which accepts two parameters, a Regular Expression, and a Replacement String.
- To remove the leading zeros, pass a Regex as the first parameter and empty string as the second parameter.
- This method replaces the matched value with the given string.
Below is the implementation of the above approach:
Python
# Python3 Program to implement
# the above approach
import re
# Function to remove all leading
# zeros from a given string
def removeLeadingZeros(str):
# Regex to remove leading
# zeros from a string
regex = "^0+(?!$)"
# Replaces the matched
# value with given string
str = re.sub(regex, "", str)
print(str)
# Driver Code
str = "0001234"
removeLeadingZeros(str)
Output
1234
Time Complexity: O(N), where N is the length of the string.
Auxiliary Space: O(1)
Remove leading zeros from a Number given Using Built in methods
use the built-in string method lstrip to remove leading zeros. This method removes all leading characters that match a specified set of characters from a string. To remove leading zeros, we can pass '0' as the set of characters to remove.
Here is an example of how to use lstrip to remove leading zeros from a string:
Python
def remove_leading_zeros(num):
return num.lstrip('0')
print(remove_leading_zeros('0001234')) # Output: '1234'
print(remove_leading_zeros('00000000')) # Output: ''
Time complexity: O(N)
Auxiliary space: O(1), where N is the length of the string.
Please refer complete article on Remove leading zeros from a Number given as a string for more details!
Similar Reads
Python Tutorial - Learn Python Programming Language Python is one of the most popular programming languages. Itâs simple to use, packed with features and supported by a wide range of libraries and frameworks. Its clean syntax makes it beginner-friendly. It'sA high-level language, used in web development, data science, automation, AI and more.Known fo
10 min read
Python Interview Questions and Answers Python is the most used language in top companies such as Intel, IBM, NASA, Pixar, Netflix, Facebook, JP Morgan Chase, Spotify and many more because of its simplicity and powerful libraries. To crack their Online Assessment and Interview Rounds as a Python developer, we need to master important Pyth
15+ min read
Python OOPs Concepts Object Oriented Programming is a fundamental concept in Python, empowering developers to build modular, maintainable, and scalable applications. By understanding the core OOP principles (classes, objects, inheritance, encapsulation, polymorphism, and abstraction), programmers can leverage the full p
11 min read
Python Projects - Beginner to Advanced Python is one of the most popular programming languages due to its simplicity, versatility, and supportive community. Whether youâre a beginner eager to learn the basics or an experienced programmer looking to challenge your skills, there are countless Python projects to help you grow.Hereâs a list
10 min read
Python Exercise with Practice Questions and Solutions Python Exercise for Beginner: Practice makes perfect in everything, and this is especially true when learning Python. If you're a beginner, regularly practicing Python exercises will build your confidence and sharpen your skills. To help you improve, try these Python exercises with solutions to test
9 min read
Python Programs Practice with Python program examples is always a good choice to scale up your logical understanding and programming skills and this article will provide you with the best sets of Python code examples.The below Python section contains a wide collection of Python programming examples. These Python co
11 min read
Python Introduction Python was created by Guido van Rossum in 1991 and further developed by the Python Software Foundation. It was designed with focus on code readability and its syntax allows us to express concepts in fewer lines of code.Key Features of PythonPythonâs simple and readable syntax makes it beginner-frien
3 min read
Python Data Types Python Data types are the classification or categorization of data items. It represents the kind of value that tells what operations can be performed on a particular data. Since everything is an object in Python programming, Python data types are classes and variables are instances (objects) of thes
9 min read
Input and Output in Python Understanding input and output operations is fundamental to Python programming. With the print() function, we can display output in various formats, while the input() function enables interaction with users by gathering input during program execution. Taking input in PythonPython input() function is
8 min read
Enumerate() in Python enumerate() function adds a counter to each item in a list or other iterable. It turns the iterable into something we can loop through, where each item comes with its number (starting from 0 by default). We can also turn it into a list of (number, item) pairs using list().Let's look at a simple exam
3 min read