5.21. Group Work: Functions and Strings

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Note

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Learning Objectives

Students will know and be able to do the following.

Content Objectives:

• Recognize strings.

• Use string indices.

• Understand how slice works for both positive and negative indices.

• Use input and convert between strings and numbers.

• Recognize common string methods.

Process Objectives:

• Predict the output from code.

• Modify code to produce the correct output.

A string is a sequence of characters enclosed in quotes. In Python you can use pairs of single or double quotes to enclose a string. You can even use tripe quotes when a string covers more than one line.

5.21.1. String Indices

Run the code below to see what it prints. Then fix it to pass the given test. It should return a string with the first character of the first name and first character of the last name.

# function definition def get_initials(first, last): return first[0] + last[-1] # function definition def main(): print(type("Hello")) print(type('Class')) print(type(42)) print(get_initials("J'Quan",'Alik')) # function call main() from unittest.gui import TestCaseGui class myTests(TestCaseGui): def testOne(self): self.assertEqual(get_initials("J'Quan",'Alik'),"JA",'''get_initials("J'Quan",'Alik')''') myTests().main()

Note

Use [index] to get a character from a string. The first character in a string is at index 0 and the last is at the length of the string minus 1 (also know as index -1 in Python). Also note that you can use pairs of single quotes or double quotes to create a string. This is useful when the string includes a single quote.

Fix the function get_initials above to return a string with the first letter of the first name followed by the first letter of the last name.

5.21.2. String Slices

Run the code below to see what it prints.

# function definition def get_short_name(first, last): print(len(first)) print(len(last)) return first[:2] + last[-2:] # function definition def main(): print(get_short_name('Simona',"Jacobs")) # function call main()

Note

Use the slice [start:end] operator to get a slice (substring) from a string. It will return a new string starting at the start and including all the characters up to just before the end (end - 1).

Write a function join_no_first that takes two strings a and b and returns a new string with all the characters in string a except the first one followed by all the characters in b except the first one. For example, join_no_first('hi', 'bye') would return 'iye'.

def join_no_first(a, b): ==== from unittest.gui import TestCaseGui class myTests(TestCaseGui): def testOne(self): self.assertEqual(join_no_first('hi', 'bye'), 'iye', "join_no_first('hi', 'bye')") self.assertEqual(join_no_first('abc', 'cba'), 'bcba', "join_no_first('abc', 'cba')") self.assertEqual(join_no_first('Watch out', 'bye'), 'atch outye', "join_no_first('Watch out', 'bye')") self.assertEqual(join_no_first('123', '456'), '2356', "join_no_first('123', '456')") self.assertEqual(join_no_first('!Hi', 'Bye!'), 'Hiye!', "join_no_first('!Hi', 'Bye!')") self.assertEqual(join_no_first('a', 'x'), '', "join_no_first('a', 'x')") myTests().main()

5.21.3. Input and Converting Between Strings and Numbers

Run the code below to see what it prints.

from datetime import datetime # function definition def get_name(): first = input("What is your first name?") print("Hello " + first) age_str = input("What is your age?") today = datetime.today() age = int(age_str) birth_year = today.year - age print("You were born in " + str(birth_year) + " or " + str(birth_year - 1)) # function call get_name()

5.21.4. String Methods

Strings have methods (functions) that operate on a string object using dot-notation as shown in the example code below.

Run the code below to see what it prints.

# function definition def get_user_name(first, last): print(first.lower()) print(last.upper()) print(last.replace("f", "1")) user = first.lower() + "_" + last.lower() return user # function definition def main(): print("run away!".capitalize()) print(get_user_name("Malana", "Coffy")) # function call main()

Note

Strings are immutable, which means that they do not change. String methods that appear to change a string return a new string.

Q-17: Drag each string method to the description of what it does. Read the chapter on strings and try again
• replace
• Returns a new string with all instances of the first specified character replaced with the second specified character.
• lower
• Returns a new string with all of the characters in lowercase.
• split
• Returns a list of strings created by splitting the original string at the specified character.
• capitalize
• Returns a new string with just the first letter capitalized (uppercase).

Run the code below to see what it prints.

# function definition def test(the_string): print(len(the_string)) s1 = the_string.strip() print(s1) print(len(s1)) print(the_string.find('H')) # function definition def main(): test(" Help! ") test(" how are you? ") # function call main()

Q-19: Drag each string method to the description of what it does. Read the chapter on strings and try again
• strip
• Returns a new string with leading and trailing spaces removed.
• find
• Returns the starting index of a target string if found or -1 if not found.

For more information on string methods see https://www.w3schools.com/python/python_ref_string.asp.

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