Python Programming Essentials - M8 - String Methods

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Common String Methods
Pavan Verma
Python Programming Essentials
@YinYangPavan

© SkillBrew http://skillbrew.com
Common String Methods
 upper()
 lower()
 capitalize()
 startswith()
 endswith()
 strip()
 find()
 split()
 join()
2

upper, lower, capitalize
3
message = "enter the dragon"
print message.upper()
print message.lower()
print message.capitalize()
Outputs:
ENTER THE DRAGON
enter the dragon
Enter the dragon
upper(): Converts all
lowercase letters in string to
uppercase
lower(): Converts all
uppercase letters in string to
lowercase
capitalize():
Capitalizes first letter of
string

startswith
4
startswith(text)
• Checks whether the string starts with text
• Return’s True if there is a match otherwise False
>>> str = "explicit is better than implicit"
>>> str.startswith('explicit')
True
>>> str.startswith('Explicit')
False
>>>

startswith (2)
5
str.startswith(text, begin, end)
startswith()optionally takes two arguments begin and
end
• text − This is the string to be checked
• begin − This is the optional parameter to set start index of
the matching boundary
• end − This is the optional parameter to set start index of
the matching boundary

startswith (3)
6
str = "explicit is better than implicit“
>>> print str.startswith("is", 9)
True
>>> print str.startswith("better", 12, 18)
True
startswith()returns True if matching string found else
False

endswith
7
>>> str = "explicit is better than implicit"
>>> str.endswith("implicit")
True
>>> str.endswith("implicit", 20)
True
>>> str.endswith("implicit", 25)
False
>>> str.endswith("than", 19, 23)
True
endswith(text)works the same way as startswith difference
being it checks whether the string ends with text or not

message = " enter the dragon "
print message.strip()
Output:
enter the dragon
message = "--enter the dragon--"
print message.strip(‘-’)
Output:
enter the dragon
strip(chars):
• returns a copy of the
string with leading and
trailing characters
removed
• If chars is omitted
or None, whitespace
characters are
removed
strip
8

message.lstrip()
Output:
'enter the dragon'
message.lstrip('-')
Output:
'enter the dragon--'
lstrip(chars):
string with leading
characters removed
or None, whitespace
characters are
removed
lstrip
9

message.rstrip()
Output:
' enter the dragon'
message.rstrip('-')
Output:
'--enter the dragon'
rstrip(chars):
string with trailing
characters removed
or None, whitespace
characters are
removed
rstrip
10

11
SPLITTING AND JOINING
STRINGS

Splitting
12
message = "enter the dragon"
print message.split()
Output:
['enter', 'the', 'dragon']
split()returns a list of words of the string

Splitting (2)
13
message = "enter-the-dragon"
print message.split('-')
Output:
['enter', 'the', 'dragon']
split(delimiter)
delimiter: character or characters which we want to
use to split the string, by default it will be space

Joining
14
seq_list = ['enter', 'the', 'dragon']
print ''.join(seq_list)
Output:
enter the dragon
str.join()
returns a string in which the string elements of sequence have
been joined by str separator

Joining (2)
15
seq_tuple = ('enter','the','dragon')
print '-'.join(seq_tuple)
Output:
enter-the-dragon

splitting/joining example
16
Lets say you have a link
'foo.com/forum?filter=comments&num=20'
1. You have to separate out the querystring from
url
2. You have to then separate out key-value pairs in
querystring
3. Now update the filter to views and num to 15
and form the url again

splitting/joining example (2)
17
>>> link = 'foo.com/forum?filter=comments&num=20'
>>> components = link.split('?')
>>> components
['foo.com/forum', 'filter=comments&num=20']
>>> url = components[0]
>>> qs = components[1]
>>> url
'foo.com/forum'
>>> qs
'filter=comments&num=20'
Step 1
Split the link using '?' as
delimiter to separate out
url and querystring

18
>>> qs
'filter=comments&num=20'
>>>params = qs.split('&')
>>> params
['filter=comments', 'num=20']
Step 2
Split the querystring
using '&' as delimiter

19
>>> params
['filter=comments', 'num=20']
>>> params[0] = 'filter=views'
>>> params[1] = 'num=15'
>>> params
['filter=views', 'num=15']
>>> qs = '&'.join(params)
>>> qs
'filter=views&num=15'
Step 3
Update the parameters and
join them using '&' as
delimiter to form
querystring

20
>>> url
'foo.com/forum'
>>> qs
'filter=views&num=15'
>>> '?'.join([url, qs])
'foo.com/forum?filter=views&num=15'
>>> link = '?'.join([url, qs])
>>> link
'foo.com/forum?filter=views&num=15'
Step 4
join url and querystring
using '?' as delimiter

Summary
 upper, lower, capitalize
 startswith and endswith
 strip, lstrip and rstrip
 splitting and joining strings
21

Resources
 String methods python docs
http://docs.Python.org/2/library/stdtypes.html#string-
methods
22

Python Programming Essentials - M8 - String Methods

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