Main Points: - Working with strings. - Problem Solving. Programming Training Main Points: - Working with strings. - Problem Solving.

Working with Python String General facts about strings: str  datatype for Python strings. A string is a sequence of characters between “”. input() returns string Operations on strings str1 + str2  new strings which concatenates two strings str1 * nr  new string which clones str1 nr times str1 in str2  test if str1 is in str2 Indexing / slicing str is a string with n characters str1[i]  String formed only with character I str1[i1:i2]  Slice of str with all the characters between i1 and i2-1. str1[i1:]  Slice with all the characters from i1

Working with Python String Functions on strings  MUST IMPORT string len(str1)  the length of str1 or number of characters. str1 in str2  finds whether str1 is in str2. str2.count(str1)  counts how many times str1 occurs in str2. str1.split(“ch”)  splits str1 in strings on the ch charter str1.joint(list)  makes a new string by 1) joining all list elements 2) separating them using str1 str1.upper() or str1.lower() or str1.dropcase()  to change the letters case

Working with Python String Functions on strings  MUST IMPORT string string.ascii_letters string.ascii_lowercase string.ascii_uppercase string.punctuation string.digits are default strings with all mention elements.

Invert a String Inverting a string requires to form a new string with the letters of the first one in reverse. Algorithmic approach: Start from an empty string. Traverse the input string in reverse Append the current letter to the new string Python approach rev_str = str1[::-1]

Invert a Sentence Inverting a sentence requires you to invert the order of words in a sentence but preserving the words. Example: “Sabin is teaching the MPT class”  ‘class MPT the teaching is Sabin’ Some questions: 1) how we can acquire the words?  split the string 2) traverse the words in reverse  no problem 3) deal with the ‘.’ if any  just remove it from there e.g. str.remove(‘.’, ‘’) Steps to solve the problem: 1) input the sentence and remove the ‘.’ if there. 2) split the sentence in words. 3) traverse the word list in reverse and add the current word to the new string. 4) add the ‘.’

Invert a Sentence Functions to work with: str2.split() str2.replace(str1, str2) str1 + str2 Better Python solution: ' '.join(str1.replace('.', '').split()[::-1]) Try to understand?

Counting Stuff in a String This requires you to find how many characters are alphabetical, numerical or space. Is str1 is a single character string then you can test its nature str1.isalpha() str1.isdigit() str1.isspace() etc It is a simple counting problem in which: Initialise the counting variables Traverse the string Test the nature of the current character and count

To do List Solve the HW problems. Read more about Strings