Homework for Week 7
After this week you can
- Perform common operations with string characters and strings
- Loop through a string
- Use Python's string functions
Strings
Python comes with a robust set of tools for text processing, the basis for which is the string data type. A string is a sequence of characters. We can read, index, slice, loop over, concatenate, compare, modify, strip, parse strings, as well as perform many other operations with them. Strings are often used in conjunction with files which we look at next week.
Watch the videos:
Slides in English
Textbook in English
Quiz
Go to Moodle and solve the quiz on strings.
Examples
Strings are useful in situations where we need to process textual data.
Personal identification code
Estonian personal identification code is a number that is unique for each citizen. The national ID card, its associated certificates, and digital signatures use personal identification codes. The code contains information about the person's gender and date of birth. Since the personal identification code is unique, it is possible to identify persons by their codes.
The code consists of 11 digits, generally written without whitespaces or other delimiters. It has the form GYYMMDDSSSC, where G shows the gender and birth century (odd numbers for male, even numbers for female; 1-2 for individuals born in the 19th century, 3-4 for the 20th century, and 5-6 for the 21st century). SSS is a serial number uniquely identifying people born on the same date, and C is the checksum digit.
The following program prompts the user for an identification code, finds the person's birth date from the code, and prints it out in the format dd.mm.yyyy:
code = input("Please enter a personal identification code: ")
#For example: 48007140350
date = code[5] + code[6]
month = code[3] + code[4]
if code[0] == "1" or code[0] == "2":
century = "18"
elif code[0] == "3" or code[0] == "4":
century = "19"
else:
century = "20"
year = century + code[1] + code[2]
print("The birthday of the person with the code", code, "is", date+"."+month+"."+year)
Note the use of + operations here, both in standalone expressions and in the print statement.
Room number from address
The following program prompts for an address. The program finds and prints the room number in the address, assuming that the address is entered in the form of street_name building_number-room_number, town_name; e.g., Narva mnt 18-2039, Tartu.
address = input("Enter address: ")
fpos = address.find("-")
lpos = address.find(",", fpos)
room = address[fpos+1:lpos]
print("Room number is", room)
The find command allows performing sequential searches in a string. Each subsequent search begins at the position where the previous search ended. This method can be used to search file content, for example, in web scraping.
Exercises
1. Name and grades
Write a program that asks the user for his/her first name and grades. The grades are entered as a continuous string of letters. The program outputs exactly four lines of text:
- Name and all grades. Regardless of how the data are entered, in the output, the name should begin with a capital letter, followed by lowercase letters, and the grades should be printed in all uppercase.
- Total number of grades
- The last grade in the input
- Total number of A's and B's, counted together
Example of program output:
Enter first name: hElEnA
Enter grades: aaAbBcDaD
Hello Helena, your grades are AAABBCDAD
You have 9 grades
Last grade is D
The number of A's and B's is 6
2. Password
The following flowchart shows an algorithm for a web page registration form. Write a program that implements the process described in the flowchart.
Reversing the password means writing it backwards: drowssap.
Example
Enter username: Username
Enter password: Password
Enter password again: Password
The password must contain both letters and numbers! Try again.
Enter password: Password2
Enter password again: Password2
The password is 2drowssaP
Make sure that the program corresponds exactly to the flowchart: the program must first ask the user for three inputs, as shown in the flowchart, even if in some cases the error in the password can be detected already after entering the password for the first time. After informing the user about the mistake, the program needs to prompt only for the password (twice).
Submit your solutions
Submit your solutions of exercises 1 and 2 in Moodle under the names home1.py and home2.py, respectively.