Perl ＆ Python: String Datatype

Xah Lee, 2005-01-09, 2011-07-22

Python

Strings are enclosed using single quote or double quote. e.g.

a="this "
b='and that'
print a, b

You can use \n for linebreak, and \t for tab, etc.

a="this\nthat\n" # use \n for line break
b='more\nthings' # single quote works too
print a, b

To quote a string of multiple lines, use triple quotes. Example:

d="""this
will be printed
in 3 lines"""
print d

You can add r to front for “raw string”. That is, backslash characters will be interpreted as is, not as escapes.

c=r"this\n and that"
print c # prints a single line

Summary:

'Single' quote and "double" quote chars are equivalent. (Linebreak in your string is not allowed. It's syntax error.)
The backslash char is used as a char escape mechanism.
If you want literal string with no backslash interpretation, prefix r in front of your quoting char, like this: r"hot".
If you want to include newline in your string, use triple 'single' quote or triple "double" quote. You can still prefix r in front.

Perl

Use single quote for literal string.

# use single quote for literal string
$a='this and
 that';
print $a; # result will contain line break

To have characters \n for newline and \t for tab, use double quote.

$a="this\nand that";
print $a; # result will contain line break

When double quote is used, variables inside the string will be evaluated.

$a=4;
$b = "this is $a";
print $b; # prints “this is 4”

Basically, perl has 2 modes of strings: single quote and double quote. In single quote mode, everything is literal. In double quote mode, backslash is a char escape mechanism, and variables inside it will be evaluated.

“q()” and “qq()” Functions

You can also use the syntax q(this n that), which is equivalent to 'this n that'. The parenthesis can be curly brackets {} or square brackets [].

# the following are all identical
$a = q(this 'n' that);
$b = q[this 'n' that];
$c = "this 'n' that";
$d = 'this \'n\' that';
print $a, "\n";
print $b, "\n";
print $c, "\n";
print $d, "\n";

Similarly, double quote is equivalent with qq().

# perl

$a=q(here, everything is literal, 
$what or \n or ' or " or not.);

$b=qq[here, variables $a will be
expanded, backslash act as escape \n (and "quotes" or parenthesis needn't be escaped).];

print $a, "\n";
print '-----------', "\n";
print $b, "\n";