Page 365 - Computer Science V2.0 Class 11

● On execution of line 9, the two strings may comprise a mix of upper and lowercase characters, we first construct a
string of lowercase characters.
● Line 10, we find the length (lengthSubstr) of the substring.
● On execution of lines 11–13, The for-loop looks for a substring of length lengthSubstr that matches the given
substr.
● Line 13, if substr is found, the function returns True and False otherwise at line 14.

Program 12.3 Searching for a substring in another string.

01 def isSubString(string, substr):
02 '''
03 Objective: To search for a substring in given string
04 Input Parameters:
05 substr - string value
06 string - string value
07 Return value: True- if substr is present in string, False, otherwise
08 '''
09 substr, string = substr.lower(), string.lower()
10 lengthSubstr = len(substr)
11 for index in range(len(string)):
12 if substr == string[index:index+lengthSubstr]:
13 return True
14 return False
12.4.4 Constructing the Reverse of a Given String

Let us develop a function reverseStr() that takes a string as an input parameter.
● Line 8, we initialize the string comprising characters in reverse order (revString) to an empty string.
● Line 9, we find the length of string (lengthSubstr).
● On execution of lines 10–11, we scan the string and append every subsequent letter to the beginning of the revString.
● On execution of line 12, finally, the function returns the reversed string (revString).

Program 12.4 Constructing the reverse of a string.

01 def reverseStr(string):
02 '''
03 Objective: To reverse the given string
04 Input Parameters:
05 string - string value
06 Return value: reverseStr- reversed string
07 '''
08 revString = ''
09 lengthSubstr = len(string)
10 for char in string:
11 revString = char + revString
12 return revString
On executing the Python module stringFns.py and invoking the appropriate functions, Python responded as
follows:
>>> distinct('Computer Science')
'computer sin'
>>> findCommon('Shekhar', 'Shayna')
3
>>> isSubString('Python programming', 'program')
True
>>> reverseStr('Python')
'nohtyP'

Strings 351