Literal strings in Python are delimited by quotes:

>>> 'This is a string'

You can use single quotation marks, as we have above. Or you can use double quotation marks, as shown below:

>>> "This is also a string"

You must, however, be consistent. For example, you can't use a double quotation mark paired with a single quotation mark:

>>> "inconsistent'
  File "<stdin>", line 1
    "inconsistent'
                  ^
SyntaxError: EOL while scanning string literal

Supporting both quoting styles allows you to easily incorporate the other quote character into the literal string without resorting to ugly escape character gymnastics:

>>> "It's a good thing."
"It's a good thing."
>>> '"Yes!", he said, "I agree!"'
'"Yes!", he said, "I agree!"'

Notice that the REPL exploits the same quoting flexibility when echoing the strings back to us.