String?
In computer science, a string is a piece of text or a collection of characters.
String Length?
The
length of a string represents the
number of characters it contains. In pyhon you can use the function
len() to find out the length of a string.
pasword = input("Enter your password:")
if len(password)<8:
print("Your password is not long enough!")
String Slicing?
On occasions, you will want your program to
extract a few characters from a string. This is called
string slicing.
You may for instance extract the first 5 characters of a phone number to retrieve the area code. Or you may need to extract the last 4 characters of a date to extract the year part.
Extracting a single character at a given position:
You can retrieve a character at a given position as follows:
string[position]
alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
firstCharacter = alphabet[0]
lastCharacter = alphabet[25]
Note: The first character is always at position 0!
Extracting a substring (multiples characters) from a string:
To slice a string in python you have to think about the starting position and the ending position and use the following syntax:
string[start:end]
This syntax will extract all the characters from position start up to but not including position end.
If start is left empty, the substring will start from position 0.
If end is left empty, the substring will end at the last character of the string.
A negative start value or end value is used to identify a position (number of characters) from the end of the string. This can be useful to extract the last few characters of a string.
Try it yourself
Enter a string below and use the two handles to change the start and end position and slice your string accordingly. The resulting substring will appear in purple.
Slicing the alphabet:
alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
print("The first 5 letters of the alphabet are: " + alphabet[:5])
print("The last 5 letters of the alphabet are: " + alphabet[-5:])
print("The letters in between are: " + alphabet[5:-5])
Slicing a date:
date = "05 January 2019"
day = date[:2] #First 2 characters
year = date[-4:] #Last 4 characters
month = date[3:-5] #The remaining characters in the middle
Locating if a substring is in a string (and retrieving its position)?
You can easily find if a substring is in a string using the keyword
in.
dateOfBirth = "15 January 2000"
if "January" in dateOfBirth:
print("You were born in January!")
You can also retrieve the exact position of a substring in a string using the find() function:
alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
pos = alphabet.find("C")
print("Letter C is at position: " + str(pos))
This script would tell us that letter “C” is at position 2. (Even though it is the third letter of the alphabet). That’s because the first letter in a string is always at position 0, not 1!
Note that if the substring is not found in the string, the find() function will return the value -1.
String Concatenation?
The act of joining two strings together is called
string concatenation.
In Python string concatenation is done using the + sign:
firstname = "James"
print("Hello " + firstname)
Python Code:
Python Challenge
Your challenge is write a program to ask the user to enter their school username in the following format:
- Year Group Using two digits (e.g. “07” for year 7, “11” for year 11, “00” for staff members)
- 1 character for their initial (first letter of their firstname)
- The user’s lastname
- A 2-digit code: “_S” for students, “_T” for teachers, “_A” for admin staff.
For instance the following usernames are valid usernames:
07jFox_S
09kJohnson_S
11rTaylor_S
00pJones_T
00jOliver_A
Your program should read the username and decide:
Solution...
The solution for this challenge is available to full members!
Find out how to become a member:
➤ Members' Area
For this challenge you will design and write a program to play against the computer. The computer will display a random number between 1 and 100. The user will have to try to guess this number. For each guess the computer will inform the user if the number to guess is higher or lower than the user guess. The program will end once the user guess matches the number to guess.
Both a hub or a switch have the same purposes: to connect multiple computers or devices in a star topology. A hub is not as efficient as a switch and would often have less ethernet ports (e.g. typically 4 or 8 ports)
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