Strings

This lesson introduces you to the basics of strings in Python.

Python has a built-in datatype str known as a string, you can think of this as a piece of text.

1. Basic Printing of Strings

Strings can be printed to the terminal using the python print() function (we will explore functions in detail later in the course).

For example:

print("hello world!")

Prints hello world! to the terminal.

Whatever is contained between the brackets will be printed out to the terminal using double quotes "".

2. Quotes

In Python strings can be enclosed in either single quotes '...' or double quotes "..."

For example:

print('hello world!')

Also prints hello world! to the terminal as per section 1.

NOTE: Although we can use both, please stick to double quotes as most languages represent strings with double quotes!

3. Escape Characters

My first program was "Hello World!" in Python

Try the following in the terminal.

print("My first program was "Hello World!" in Python")

You will see a SyntaxError: invalid syntax, this is the Python interpreter telling you that it does not understand the code you have entered. If you look closely you will see that it is pointing to the H, the character after the second "". This is because it is illegal to put a double quote character " within a string.

To fix this we need to use an escape character, in Python, this is the \ (backslash) followed by a particular character.

Amend the previous line of code to include backslashes for the quotes in the string.

print("My first program was \"Hello World!\" in Python")

If you run this you will now get the desired output My first program was "Hello World!" in Python.

There are a number of special escape characters in Python, you can look them up. We will just look at the following:

For example,

print("My first program was \"Hello World!\" in Python\n\nPython is cool!")

prints out :

My first program was "Hello World!" in Python
  
Python is cool!

4. Multiline Strings

Multiline strings let us write multiple lines in a string without escape characters or multiple print statements. In Python, they start with ''' or """ and end the same way.

numbers = '''3
5
6
7
'''  
print(numbers)

The above will print out the following to the terminal.

3
5
6
7

If you have an escape character in your multiline string and you want this to appear in the terminal you should escape it with another \.

For example,

print('''This is a multiline string.

The tab escape character in python is \t.
''')

will result in the output:

This is a multiline string.

print('''This is a multiline string.

The tab escape character in python is   .
''')

i.e. it will put a tab into the output. To get \t to show up you need to escape it with another \ as follows:

print('''This is a multiline string.

The tab escape character in python is \\t.
''')

NOTE: This is the same in a normal string. To output an escape character as text you should escape it!

5. Concatenating Strings

To concatenate, or combine, strings you can use the + operator.

For example,

str1 = "Hello"
str2 = "World!"

print(str1 + str2)

results in the output:

HelloWorld!

To get the standard Hello World! we could do the following.

str1 = "Hello"
str2 = "World!"

print(str1 + " " + str2)

Note that you can also just concatenate strings within the print function:

print("Hello" + " " + "World")

6. Formatting Strings

We can also combine strings using the format() method.

The format() method takes the passed arguments and puts them in the string where the placeholders {} are:

For example,

str1 = "string 1"
str2 = "string 2"
print("Hello {} and hello {}.".format(str1, str2))

results in the output:

Hello string 1 and hello string 2.

We can also achieve this using index numbers starting at {0}

str1 = "string 1"
str2 = "string 2"
print("Hello {0} and hello {1}.".format(str1, str2))

This is especially useful if you wish to repeat strings stored in variables.

For example,

str1 = "string 1"
str2 = "string 2"
print("Hello {0} and hello {1}.\nBye {0} and bye {1}.".format(str1, str2))

results in the output:

Hello string 1 and hello string 2.
Bye string 1 and bye string 2.

7. f-Strings

Since Python 3.6 you can use f-Strings (formatted string literals), we will use these throughout the course, but you should understand how to use the others in case someone else has written code using them.

We can achieve the previous output by doing the following:

str1 = "string 1"
str2 = "string 2"
print(f"Hello {str1} and hello {st2}.\nBye {str1} and bye {str2}.")

which again results in the output:

Hello string 1 and hello string 2.
Bye string 1 and bye string 2.

Note that in front of the string we put an f. This tells python that anything in curly braces should be evaluated. So in the example above, the values of str1 and str2 are substituted into the string.

=== TASK ===

Create a new Python file.

1. Print Programming in Python to the terminal.  

2. Print Programming in Python with single quotes to the terminal using single quotes ''.

3. Print the following to the terminal.

I know how to put "quotes" into a string.
  
And put in new lines!

4. Using a multiline string print

I am using a multiline string to:
- print multiple lines 
- without the use of the escape character \n

to the terminal.

5. Create the following strings and store them in the variables str1 and str2

str1 = "string 1"
str2 = "string 2"

Print Hi, I am string 1 and I am string 2! to the terminal using string concatenation.

6. Print string 1 is before string 2 and string 2 is after string 1 to the terminal using f-strings.

The entire output of the program should be as follows:

Programming in Python
Programming in Python with single quotes
I know how to put "quotes" into a string.

And put in new lines!
I am using a multiline string to:
- print multiple lines
- without the use of the escape character \n
Hi, I am string 1 and I am string 2!
string 1 is before string 2 and string 2 is after string 1