2. Page 1
Agenda
• Escape Sequences
• Raw Strings
• Doc Strings
• More formatting
• Conversions
• String Methods
• The string module
3. Page 2
Escapes and Special Characters
• Certain special characters have special values
• They do not have a corresponding print character
• Instead they have an effect
• For example, newline, carriage return
• To insert a special character, you “escape” it
• Using the backslash
5. Page 4
Raw Strings
• The raw_input( ) function reads a line from
standard input as a raw string
• Used in interactive console programs
6. Page 5
Quoting
• Can use either single or double
• This makes embedded quotes easy
• Can also “escape” characters with
• Triple quotes define “long strings”
• String that can span multiple lines
• Often used in documentation and web pages
7. Page 6
str( ) vs. repr( )
• str( ) converts an object to a string
• It renders a human-readable string
• print uses str( ) (and expands escapes)
• repr( ) renders a string that can be evaluated by the
interpreter
• As if typed at the >>> prompt
• So it executes correctly
• Also can use backquotes
• The interpreter uses repr( ) to echo variables
• Differences show up in numbers and escape
sequences
8. Page 7
str( ) vs. repr( )
Examples
>>> x = .1
>>> x
0.10000000000000001
>>> str(x)
'0.1‘
>>> repr(x)
'0.10000000000000001‘
>>> `x`
'0.10000000000000001‘
>>> s = "Hellonthere"
>>> s
'Hellonthere'
>>> print s
Hello
there
>>> repr(s)
"'Hellonthere'"
10. Page 9
Format Descriptors
• %s (string, via str( ))
• %r (string, via repr( ))
• %c (character)
• %d (decimal integer)
• %x (hex integer)
• %X (uppercase hex)
• %e (scientific notation for reals)
• %f (fixed-point decimal for reals)
• %g (attempts %f; bails to %e)
11. Page 10
String Methods
• A lot!
• Called as <string-var>.<method>(…)
• For example, s.count('a')
• capitalize, center, count, endswith, find,
index, isalpha, isdigit (etc., as in C), istitle,
join, lower, replace, split, strip, swapcase,
title, translate, upper, zfill
12. Page 11
Using split( )
• Splits a string into substrings
• Uses whitespace as a separator(default)
• You can provide your own separator
• It uses the whole separator string
• See next slide
• The re module has a better version of split
13. Page 12
Using split( ) and join( )
Example
>>> s = 'a,b,c d,e‘
>>> s.split()
['a,b,c', 'd,e']
>>> s.split(',')
['a', 'b', 'c d', 'e']
>>> ','.join(['x','y','z'])
'x,y,z‘
>>> ''.join(['x','y','z'])
'xyz'
14. Page 13
Exercise
• Print the words from a sentence in the
reverse order of the appearance,
• Write a module that reads a string from the
console and tests to see if it is a palindrome
(spelled the same backward as forward)
(Hint: for both of these, the reverse( ) list method comes in
handy)
