You can use Python 3.6's f-strings for variables inside multi-line or lengthy single-line strings. You can manually specify newline characters using \n.

Variables in a multi-line string

string1 = "go"
string2 = "now"
string3 = "great"

multiline_string = (
    f"I will {string1} there\n"
    f"I will go {string2}.\n"
    f"{string3}."
)

print(multiline_string)

I will go there
I will go now
great

Variables in a lengthy single-line string

string1 = "go"
string2 = "now"
string3 = "great"

singleline_string = (
    f"I will {string1} there. "
    f"I will go {string2}. "
    f"{string3}."
)

print(singleline_string)

I will go there. I will go now. great.

Alternatively, you can also create a multiline f-string with triple quotes where literal newlines are considered part of the string. However, any spaces at the start of the line would also be part of the string, so it can mess with code indentation.

multiline_string = f"""I will {string1} there.
I will go {string2}.
{string3}."""

Python 3: Formatted Strings

As of Python 3.6 you can use so-called "formatted strings" (or "f strings") to easily insert variables into your strings. Just add an f in front of the string and write the variable inside curly braces ({}) like so:

>>> name = "John Doe"
>>> f"Hello {name}"
'Hello John Doe'

To split a long string to multiple lines surround the parts with parentheses (()) or use a multi-line string (a string surrounded by three quotes """ or ''' instead of one).

1. Solution: Parentheses

With parentheses around your strings you can even concatenate them without the need of a + sign in between:

a_str = (f"This is a line \n{str1}\n"
         f"This is line 2 \n{str2}\n"
         f"This is line 3")  # no variable in this line, so a leading f"" is optional but can be used to properly align all lines

Good to know: If there is no variable in a line, there is no need for a leading f for that line.

Good to know: You could achieve the same result with backslashes (\) at the end of each line instead of surrounding parentheses but accordingly to PEP8 you should prefer parentheses for line continuation:

Long lines can be broken over multiple lines by wrapping expressions in parentheses. These should be used in preference to using a backslash for line continuation.

2. Solution: Multi-Line String

In multi-line strings you don't need to explicitly insert \n, Python takes care of that for you:

a_str = f"""This is a line
        {str1}
        This is line 2
        {str2}
        This is line 3"""

Good to know: Just make sure you align your code correctly otherwise you will have leading white space in front each line.

By the way: you shouldn't call your variable str because that's the name of the datatype itself.

Sources for formatted strings:

• What's new in Python 3.6
• PEP498

Try this

message = """
          Hello, %(foo)s
          Sincerely, %(bar)s
          """ % {'foo': "John", 'bar': "Doe"}