Strings are amongst the most popular types in Python. We can create them simply by enclosing characters in quotes. Python treats single quotes the same as double quotes. Creating strings is as simple as assigning a value to a variable.For example −
var1 = "Hello world"
var2 = "Python programing"
Accessing Values in Strings
Python does not support a character type; these are treated as strings of length one, thus also considered a substring.
To access substrings, use the square brackets for slicing along with the index or indices to obtain your substring. For example −
#!/usr/bin/python
var1 = 'Hello World!'
var2 = "Python Programming"
print "var1[0]: ", var1[0]
print "var2[1:5]: ", var2[1:5]
When the above code is executed, it produces the following result −
var1[0]: H var2[1:5]: ytho
Updating Strings
You can "update" an existing string by (re)assigning a variable to another string. The new value can be related to its previous value or to a completely different string altogether. For example −
When the above code is executed, it produces the following result −
Updated String :- Hello Python
Escape Characters
Following table is a list of escape or non-printable characters that can be represented with backslash notation.
An escape character gets interpreted; in a single quoted as well as double quoted strings.
| Backslash notation | Hexadecimal character | Description |
|---|---|---|
| \a | 0x07 | Bell or alert |
| \b | 0x08 | Backspace |
| \cx | Control-x | |
| \C-x | Control-x | |
| \e | 0x1b | Escape |
| \f | 0x0c | Formfeed |
| \M-\C-x | Meta-Control-x | |
| \n | 0x0a | Newline |
| \nnn | Octal notation, where n is in the range 0.7 | |
| \r | 0x0d | Carriage return |
| \s | 0x20 | Space |
| \t | 0x09 | Tab |
| \v | 0x0b | Vertical tab |
| \x | Character x | |
| \xnn | Hexadecimal notation, where n is in the range 0.9, a.f, or A.F |
String Special Operators
Assume string variable a holds 'Hello' and variable b holds 'Python', then −
| Operator | Description | Example |
|---|---|---|
| + | Concatenation - Adds values on either side of the operator | a + b will give HelloPython |
| * | Repetition - Creates new strings, concatenating multiple copies of the same string | a*2 will give -HelloHello |
| [] | Slice - Gives the character from the given index | a[1] will give e |
| [ : ] | Range Slice - Gives the characters from the given range | a[1:4] will give ell |
| in | Membership - Returns true if a character exists in the given string | H in a will give 1 |
| not in | Membership - Returns true if a character does not exist in the given string | M not in a will give 1 |
| r/R | Raw String - Suppresses actual meaning of Escape characters. The syntax for raw strings is exactly the same as for normal strings with the exception of the raw string operator, the letter "r," which precedes the quotation marks. The "r" can be lowercase (r) or uppercase (R) and must be placed immediately preceding the first quote mark. | print r'\n' prints \n and print R'\n'prints \n |
| % | Format - Performs String formatting | See at next section |
String Formatting Operator
One of Python's coolest features is the string format operator %. This operator is unique to strings and makes up for the pack of having functions from C's printf() family. Following is a simple example −
#!/usr/bin/python
print "My name is %s and weight is %d kg!" % ('Zara', 21)
When the above code is executed, it produces the following result −
My name is Zara and weight is 21 kg!
Here is the list of complete set of symbols which can be used along with % −
| Format Symbol | Conversion |
|---|---|
| %c | character |
| %s | string conversion via str() prior to formatting |
| %i | signed decimal integer |
| %d | signed decimal integer |
| %u | unsigned decimal integer |
| %o | octal integer |
| %x | hexadecimal integer (lowercase letters) |
| %X | hexadecimal integer (UPPERcase letters) |
| %e | exponential notation (with lowercase 'e') |
| %E | exponential notation (with UPPERcase 'E') |
| %f | floating point real number |
| %g | the shorter of %f and %e |
| %G | the shorter of %f and %E |
Other supported symbols and functionality are listed in the following table −
| Symbol | Functionality |
|---|---|
| * | argument specifies width or precision |
| - | left justification |
| + | display the sign |
| <sp> | leave a blank space before a positive number |
| # | add the octal leading zero ( '0' ) or hexadecimal leading '0x' or '0X', depending on whether 'x' or 'X' were used. |
| 0 | pad from left with zeros (instead of spaces) |
| % | '%%' leaves you with a single literal '%' |
| (var) | mapping variable (dictionary arguments) |
| m.n. | m is the minimum total width and n is the number of digits to display after the decimal point (if appl.) |
Unicode String
Normal strings in Python are stored internally as 8-bit ASCII, while Unicode strings are stored as 16-bit Unicode. This allows for a more varied set of characters, including special characters from most languages in the world. I'll restrict my treatment of Unicode strings to the following −
#!/usr/bin/python
print u'Hello, world!'
When the above code is executed, it produces the following result −
Hello, world!
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