This document discusses various string processing techniques in Python including escape sequences, raw strings, docstrings, string formatting, conversions, and string methods. It provides examples of using escape characters, raw strings, quoting strings, the difference between str() and repr(), format descriptors, common string methods like split() and join(), and exercises for reversing words in a sentence and checking for palindromes.

1. Python-Basics
Strings-Text Processing
Guru

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

4. Page 3
Escape Characters
• Newline ('n')
• Carriage return ('r')
• Single quote (''')
• Double quote (""")
• Backspace ('b')
• Tab ('t')
• Vertical tab ('v')
• 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'"

9. Page 8
Question
• What is the result of executing:
str(2+3)
?

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)

15. Page 14
Questions

16. Page 15
Imagination Action Joy