Python – Remove leading 0 from Strings List
Last Updated : 04 Apr, 2023
Sometimes, while working with Python, we can have a problem in which we have data which we need to perform processing and then pass the data forward. One way to process is to remove a stray 0 that may get attached to a string while data transfer. Let’s discuss certain ways in which this task can be performed.
Method #1 : Using lstrip() + list comprehension
This is one of the one-liners with the help of which this task can be performed. In this, we strip the leading 0 using lstrip and the extension of logic to list is done using list comprehension.
Step-by-step approach:
- Initialize a list of strings.
- Print the original list of strings.
- Use a list comprehension to loop through each element in the list.
- For each element, use the lstrip() method to remove any leading 0s.
- Append the modified string to a new list.
- Print the new list of strings with leading 0s removed.
Below is the implementation of the above approach:
Python3
test_list = ['012', '03', '044', '09']
print("The original list is : " + str(test_list))
res = [ele.lstrip('0') for ele in test_list]
print("The string list after leading 0 removal : " + str(res))
|
Output The original list is : ['012', '03', '044', '09'] The string list after leading 0 removal : ['12', '3', '44', '9']
Time Complexity: O(N)
Auxiliary Space: O(1)
Method #2: Using startswith() + loop + list slicing
This is one of the ways in which this task can be performed. In this, we check for the initial 0 using startswith(), and then list slicing is used to remake the string excluding 0.
Python3
test_list = ['012', '03', '044', '09']
print("The original list is : " + str(test_list))
for idx in range(len(test_list)):
if test_list[idx].startswith('0'):
test_list[idx] = test_list[idx][1:]
print("The string list after leading 0 removal : " + str(test_list))
|
Output The original list is : ['012', '03', '044', '09'] The string list after leading 0 removal : ['12', '3', '44', '9']
Time Complexity: O(N)
Auxiliary Space: O(1)
Method #3 : Using find() and slicing methods
Python3
test_list = ['012', '03', '044', '09']
print("The original list is : " + str(test_list))
for i in range(len(test_list)):
if test_list[i].find('0') == 0:
test_list[i] = test_list[i][1:]
print("The string list after leading 0 removal : " + str(test_list))
|
Output The original list is : ['012', '03', '044', '09'] The string list after leading 0 removal : ['12', '3', '44', '9']
Time Complexity: O(N)
Auxiliary Space: O(1)
Method #4 : Using int() function
Python3
test_list = ['012', '03', '044', '09']
print("The original list is : " + str(test_list))
for i in range(len(test_list)):
test_list[i] = int(test_list[i])
print("The string list after leading 0 removal : " + str(test_list))
|
Output The original list is : ['012', '03', '044', '09'] The string list after leading 0 removal : [12, 3, 44, 9]
Time Complexity: O(N)
Auxiliary Space: O(1)
Method #5: Using regex Expressions
One more approach to solving this problem could be using Regular Expressions (re module). We can use the re.sub() function to search for the pattern ‘^0+’ (i.e., one or more zeros at the start of the string) and replace it with an empty string.
Python3
import re
test_list = ['012', '03', '044', '09']
print("The original list is : " + str(test_list))
res = [re.sub("^0+", "", ele) for ele in test_list]
print("The string list after leading 0 removal : " + str(res))
|
Output The original list is : ['012', '03', '044', '09'] The string list after leading 0 removal : ['12', '3', '44', '9']
Time Complexity: O(N)
Auxiliary Space: O(1)
Method #6: Using map() function
You can use the map() function to apply the int() function to each element of the list in a more concise way than using a for loop. Here’s how to use map() to remove leading zeros from strings in a list:
- Initialize a list test_list with elements as strings containing leading zeros.
- Print the original list using print() function.
- Use the map() function to apply the int() function to each element of the list in a concise way using a lambda function.
- Convert the output of map() function to list using list() function and store it in test_list.
- Print the final list with leading zeros removed using print() function.
Python3
test_list = ['012', '03', '044', '09']
print("The original list is : " + str(test_list))
test_list = list(map(lambda x: int(x), test_list))
print("The string list after leading 0 removal : " + str(test_list))
|
Output The original list is : ['012', '03', '044', '09'] The string list after leading 0 removal : [12, 3, 44, 9]
Time complexity: O(n) where n is the number of elements in the list.
Auxiliary space: O(n) because we create a new list with the same number of elements as the original list.
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