In this article we will discuss ways to remove first N characters from a string either by using slicing or regex or simple for loop.
Use slicing to remove first N character from string in python
In python, we can use slicing to select a specific range of characters in a string i.e.
str[start:end]
It returns the characters of the string from index position start to end -1, as a new string. Default values of start & end are 0 & Z respectively, where Z is the size of the string. It means if neither start nor end are provided, then it selects all characters in the string i.e. from 0 to size-1 and creates a new string from those characters.
We can use this slicing technique to slice out a piece of string, that includes all characters of string except the first N characters. Let’s see how to do that,
Remove first 3 character from string using Slicing
Suppose our string contains N characters. We will slice the string to select characters from index position 3 to N and then assign it back to the variable i.e.
org_string = "Sample String" # Slice string to remove first 3 characters from string mod_string = org_string[3:] print(mod_string)
Output
ple String
By selecting characters in string from index position 3 to N, we selected all characters from string except the first 3 characters and then assigned this sliced string object back to the same variable again, to give an effect that first 3 characters of string are deleted.
Remove first character from string using slicing
To remove the first character from string, slice the string to select characters from index 1 till the end of string i.e.
org_string = "Sample String" # Slice string to remove first 3 characters from string mod_string = org_string[1:] print(mod_string)
Output:
ample String
It selected all characters in the string except the first one.
Use for-loop to remove first N character from string in python
To delete first N character from a string, we can iterate over the characters of string one by one and select all characters from index position N till the end of the string. We have created a function for this,
def remove_first_n_char(org_str, n):
""" Return a string by deleting first n
characters from the string """
mod_string = ""
for i in range(n, len(org_str)):
mod_string = mod_string + org_str[i]
return mod_string
It accepts a string and a number N as arguments. Returns a new string that contains all the characters of the given string, except first N characters. Let’s use this function in some examples,
Remove first character from string using for loop
org_string = "Sample String" # Remove first character from string mod_string = remove_first_n_char(org_string, 1) print(mod_string)
Output
ample String
Remove first 3 characters from string using for loop
org_string = "Sample String" # Remove first character from string mod_string = remove_first_n_char(org_string, 3) print(mod_string)
Output
ple String
Remove First N character from string using regex
We can use regex in python, to match 2 groups in a string i.e.
- Group 1: First N character of string
- Group 2: Every character in string except the first N characters
Then modify the string by substituting both the groups by a single group i.e. group 2.
Remove first 3 characters from string using regex
import re
def remove_first_group(m):
""" Return only group 1 from the match object
Delete other groups """
return m.group(2)
org_string = "Sample String"
result = re.sub("(^.{3})(.*)", remove_first_group, org_string)
print(result)
Output
ple String
Here sub() function matched the given pattern in the string and passed the matched object to our call-back function remove_first_group(). Match object internally contains two groups and the function remove_first_group() returned a string by selecting characters from group 2 only. Then sub() function replaced the matched characters in the original string by the characters returned by the remove_first_group() function. So, this is how we can delete first N characters from a string in python
To remove first character from string using regex, use n as 1 i.e.
import re
def remove_first_group(m):
""" Return only group 1 from the match object Delete other groups """
return m.group(2)
org_string = "Sample String"
result = re.sub("(^.{1})(.*)", remove_first_group, org_string)
print(result)
Output
ample String
The complete example is as follows,
import re
def remove_first_group(m):
""" Return only group 1 from the match object
Delete other groups """
return m.group(2)
def remove_first_n_char(org_str, n):
""" Return a string by deleting first n
characters from the string """
mod_string = ""
for i in range(n, len(org_str)):
mod_string = mod_string + org_str[i]
return mod_string
def main():
print('*** Remove first N character from string using Slicing ***')
print('*** Remove first 3 characters from string using slicing ***')
org_string = "Sample String"
# Slice string to remove first 3 characters from string
mod_string = org_string[3:]
print(mod_string)
print('*** Remove first character from string using slicing ***')
org_string = "Sample String"
# Slice string to remove first 3 characters from string
mod_string = org_string[1:]
print(mod_string)
print('***** Remove first N character from string using for loop *****')
print('*** Remove first character from string using for loop ***')
org_string = "Sample String"
# Remove first character from string
mod_string = remove_first_n_char(org_string, 1)
print(mod_string)
print('*** Remove first 3 characters from string using for loop ***')
org_string = "Sample String"
# Remove first character from string
mod_string = remove_first_n_char(org_string, 3)
print(mod_string)
print('***** Remove first N characters from string using regex *****')
print('*** Remove first character from string using regex ***')
org_string = "Sample String"
result = re.sub("(^.{1})(.*)", remove_first_group, org_string)
print(result)
print('*** Remove first 3 characters from string using regex***')
org_string = "Sample String"
result = re.sub("(^.{3})(.*)", remove_first_group, org_string)
print(result)
if __name__ == '__main__':
main()
Output:
*** Remove first N character from string using Slicing *** *** Remove first 3 characters from string using slicing *** ple String *** Remove first character from string using slicing *** ample String ***** Remove first N character from string using for loop ***** *** Remove first character from string using for loop *** ample String *** Remove first 3 characters from string using for loop *** ple String ***** Remove first N characters from string using regex ***** *** Remove first character from string using regex *** ample String *** Remove first 3 characters from string using regex*** ple String