Assign a Name to a String¶

Learning Objectives:

Create a variable that can store text (a string)
Add (append or concatenate) strings together to create new strings
Introduce the input function and the concept of a function.
Convert a number into a string to concatenate it to another string
Use dot-notation to invoke functions on string objects
Introduce some string functions like lower, capitalize, len, and find.
Show that strings are immutable (don’t change)

Concatenating (Appending) Strings¶

Computers can use names to represent anything. In the last chapter we saw that we can name numbers (declare a variable and set its value to a number) and then do calculations using the names for the numbers. We can also name strings and do calculations with their names, too. A string is a sequence of characters enclosed in a pair of single, double, or triple quotes like 'Hi', "How are you?", or '''Why can't you do that?'''. What does it mean to do a calculation on a string? Well, Python uses the + symbol to concatenate strings as shown below. Concatenate means to create a new string with all the characters in the first string followed by all of the characters in the second string. This is also called appending strings together.

Now try running this slightly different example.

Note

Blank spaces are not automatically added when you append two strings. If you want a blank space in between two strings then put it there explicitly using a string with just a space in it " " as shown in ActiveCode1.

Try to run the example below. It should give you errors. Can you fix the errors?

Note

A string is a sequence of characters enclosed in a pair of single, double, or triple quotes. If you start a string with a single quote you must end it with a single quote. If you start a string with a double quote you must end it with a double quote. You must use the + operator to append strings together.

Getting Strings from Users¶

We can use the input function in Python to read in strings from users. For example, to get your first and last name and then print your full name. A function can take input and returns some value.

The value returned by the input function is always a string, even if it looks like something else. Use CodeLens to study the following example. Enter the single digit 7 and watch closely for the values 3 * answers and 3 + number_answer. Be sure you understand what is happening before moving on.

Concatenating Strings and Numbers¶

You can print both strings and numbers, and you can concatenate strings using +, but if you try to concatenate a string and a number you will get an error. The string "5" is stored very differently than the number 5 in computer memory, so to concatenate the number 5 and a string we need to convert the number into a string first. The str(num) function will convert a number into a string.

Note

Notice how printing the string "Fred" prints something different than printing the value of the variable Fred. Printing the string "Fred" prints the exact characters in that string. Remember that strings are enclosed in pairs of double or single quotes and when they are printed it will print the exact characters in the string. When you print a variable it will print the value of that variable.

We can update our driving example to print out the cost of the trip with just one print statement.

Check your understanding

csp-4-1-1: Given the following code segment, and assuming the user enters the single digit 7 at the prompt, what will be printed?
answer = input("What is the sum of 2 and 5? ")
print(3 + answer)
An error message
Python doesn't know how to add numbers to strings, and 3 is a number and answer is a string.

37
This would be true if both operands were strings

10
This would be true if both operands were numbers

csp-4-1-2: Given the following code segment, what will be printed?

street = "125 Main Street"
print("The address is " + "street")

The address is street
Since street is in double quotes it will print the string street rather than the value of the variable street.
The address is 125 Main Street
This would be true if it was print("The address is " + street)
It won't execute
While this isn't printing what we probably want it to, it will print something.

csp-4-1-3: What will be printed when the following executes?

street = "125 Main Street"
city_state = "Atlanta, GA"
print(street + "," + city_state)

125 Main Street, Atlanta, GA
This would be true if it was street + ", ".
125 Main Street,Atlanta, GA
There isn't a space after the comma and one isn't added automatically.
125 Main Street Atlanta, GA
What about the comma?

Next Section - Strings are Objects