Given a string, the task is to extract only alphabetical characters from a string. Given below are few methods to solve the given problem.
Method #1: Using re.split
Python3
# Python code to demonstrate# to get characters from stringimport re# initialising stringini_string = "123()#$ABGFDabcjw"ini_string2 = "abceddfgh"# printing stringsprint ("initial string : ", ini_string, ini_string2)# code to find characters in stringres1 = " ".join(re.split("[^a-zA-Z]*", ini_string))res2 = " ".join(re.split("[^a-zA-Z]*", ini_string2))# printing resultant stringprint ("first string result: ", str(res1))print ("second string result: ", str(res2)) |
initial string : 123()#$ABGFDabcjw abceddfgh first string result: A B G F D a b c j w second string result: a b c e d d f g h
Time complexity: O(n), where n is the length of the input string.
Auxiliary space: O(n), where n is the length of the input string, as the resultant string is stored in a variable.
Method #2: Using re.findall
Python3
# Python code to demonstrate# to get characters in stringimport re# initialising stringini_string = "123()#$ABGFDabcjw"ini_string2 = "abceddfgh"# printing stringsprint ("initial string : \n", ini_string, "\n", ini_string2)# code to find characters in stringres1 = " ".join(re.findall("[a-zA-Z]+", ini_string))res2 = " ".join(re.findall("[a-zA-Z]+", ini_string2))# printing resultant stringprint ("first string result: ", str(res1))print ("second string result: ", str(res2)) |
initial string : 123()#$ABGFDabcjw abceddfgh first string result: ABGFDabcjw second string result: abceddfgh
Time complexity: O(n), where n is the length of the input string
Auxiliary space: O(n), where n is the length of the input string.
Method #3: Using isalpha()
Python3
# Python code to demonstrate# to get characters in a string# if present# initialising stringini_string = "123()#$ABGFDabcjw"# printing string and its lengthprint("initial string : ", ini_string)# code to find characters in stringres1 = ""for i in ini_string: if i.isalpha(): res1 = "".join([res1, i])# printing resultant stringprint("first result: ", str(res1)) |
initial string : 123()#$ABGFDabcjw first result: ABGFDabcjw
Time complexity: O(n), where n is the length of the input string ini_string.
Auxiliary space: O(n), where n is the length of the input string ini_string.
Method #4 : Without any builtin methods
Python3
# Python code to demonstrate# to get characters in a string# if present# initialising stringini_string = "123()#$ABGFDabcjw"lower="abcdefghijklmnopqrstuvwxyz"upper="ABCDEFGHIJKLMNOPQRSTUVWXYZ"a=lower+upper# printing string and its lengthprint ("initial string : ", ini_string)# code to find characters in stringres1 = ""for i in ini_string: if i in a: res1+=i# printing resultant stringprint ("first result: ", str(res1)) |
initial string : 123()#$ABGFDabcjw first result: ABGFDabcjw
The time complexity of this program is O(n), where n is the length of the input string ini_string.
The auxiliary space required by the program is also O(n), since the program creates a new string res1 to store the characters that are present in the input string.
Method 5: Using list comprehension method
Python3
ini_string = "123()#$ABGFDabcjw"a="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"res=[i for i in ini_string if i in a]print("".join(res)) |
ABGFDabcjw
Method 6: Using enumerate function
Python3
ini_string = "123()#$ABGFDabcjw"a="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"res=[j for i,j in enumerate(ini_string) if j in a]print("".join(res)) |
ABGFDabcjw
Method #7: Using filter and lambda:
The filter function takes a function and a list-like object as input, and returns a list of elements from the input object for which the function returns True. In this case, the function is lambda x: x.isalpha(), which returns True for any alphabetical character and False for any non-alphabetical character. The join method is then used to concatenate the characters into a single string.
Python3
# Python code to demonstrate# to get characters in a string# if presentdef extract_characters(string): #Using filter to get the characters return "".join(filter(lambda x: x.isalpha(), string))# Test the functionprint(extract_characters("123()#$ABGFDabcjw")) # Output: ABGFDabcjwprint(extract_characters("abceddfgh")) # Output: abceddfgh#This code is contributed by Edula Vinay Kumar Reddy |
ABGFDabcjw abceddfgh
Time complexity: O(n)
Auxiliary Space: O(n)
Method #8:Using itertools.filterfalse() method
Python3
# Python code to demonstrate# to get characters in a string# if presentimport itertoolsdef extract_characters(string): #Using filter to get the characters return "".join(itertools.filterfalse(lambda x: not x.isalpha(), string))# Test the functionprint(extract_characters("123()#$ABGFDabcjw")) # Output: ABGFDabcjwprint(extract_characters("abceddfgh")) # Output: abceddfgh |
ABGFDabcjw abceddfgh
Time Complexity: O(N)
Auxiliary Space: O(N)
Method #9:Using str.translate() with str.maketrans()
Here is an implementation using str.translate() with str.maketrans() to remove non-alphabetic characters from a given string:
Algorithm:
Initialize the input string to be extracted from.
Create a translation table using str.maketrans() method where the second argument is all the non-alphabetic characters to be removed from the input string.
Use the translate() method to remove the non-alphabetic characters from the input string using the created translation table.
Print the output string.
Python3
# Python code to extract only alphabetical characters from a given string using str.translate() with str.maketrans()# initializing input stringinput_string1 = "123()#$ABGFDabcjw"input_string2 = "abceddfgh"# creating translation table to remove non-alphabetic characterstranslation_table = str.maketrans( "", "", "!@#$%^&*()_-+={}[]|\:;\"'<>,.?/`~1234567890")# removing non-alphabetic characters from input string using translate()output_string1 = input_string1.translate(translation_table)output_string2 = input_string2.translate(translation_table)# printing outputprint(output_string1)print(output_string2) |
ABGFDabcjw abceddfgh
Time Complexity: O(N)
Auxiliary Space: O(N)
