Python:Strings

Strings are immutable, all methods return a new string

Formatting

Basic

str1.replace(old,new[,cnt])

In str1 replace old by new (cnt times)

str1.join(list)

Join list (or set or other sequence) with str1 as separator

str1.split(sep[,max)

Split string in to a list on sep into max + 1 elements (remainder is put in last element)

str1.splitlines([keepends])

Split on newline, with keepends the newline is preserved.

str1.center(w)

str1.ljust(w)

str1.rjust(w)

Put spaces around str1 to length 'w' is reached.

str1.expandtabs(size)

Replace tabs by 'size' number of spaces

Advanced

str1.format(values)

Fill in 'values' in string-fields ({}), if numbered fields can be in a different format than the values.

If values are in a dict, they can be addressed by their key.

Code Example

 
"Value 1: {}, Value2: {}".format(1,2)
"Value 2: {1}, Value1: {0}".format(1,2)

dict1 = {'value1':1, 'value2':2}
"Value 2: {value2}, Value1: {value1}".format(dict1)

{[field]:spec}

The format can be specified after the (optional) fieldnumber.

<alignment><width>.<precision><type>

Generic format specification. Anything not needed can be left out.

Alignment

Always show sign

<	Left
>	Right
^	Center
=	Padding (after sign)
#	Prepend for x, o and b types

Types

c	Character
d	decimal
f	Float
%	Percent
o	Octal
x	Hexadecimal
b	Binary
e	Exponent
g	Python chooses between decimal, float or exponent

Searching

import re

The re modules provides Perl-like regular expression matching for string and byte objects

re1 = re.compile(regexp)

Create regular expression object to use for matching. This is more efficient if the regular expression in used several times in a program.

mo1 = re1.match(str1)

mo1 = re.match(str1,regexp)

Find 'regexp' at the beginning of 'str1'. Return match object if found, else return None-object

mo1 = re.search(str1,regexp)

Find first occurrence of 'regexp' in 'str1'. Return match object if found, else return None-object

lst1 = re.findall(str1,regexp)

Find all occurrences of 'regexp' in 'str1'. Return a list of strings.

mol1 = re.finditer(str1,regexp)

Find all occurrences of 'regexp' in 'str1'. Return a list of match objects.

Match objects

mo.group()

The matched string in match object 'mo'

mo.group(1)

First submatch (in () ) in the matched string in match object 'mo'

mo.start()

The start position of the matched string in match object 'mo'

mo.end()

The end position of the matched string in match object 'mo'

mo.span()

Tuple with start and end position of the matched string in match object 'mo'

re.search(str1,regexp,modifier)

re1 = re.compile(regexp,modifier)

Modify how matching is done

re.DOTALL

The . matches all characters (default is all characters except newline). Use for searching in web or book pages.

re.I

Ignore case

Code Example

import re
str1 = "The thing to cut in pieces"
rel1 = re.compile('h.*n')
print "Matching"
mo1 = rel1.match(str1)

if m:
 print mo1.group()
 print mo1.start()
 print mo1.end()
 print mo1.span()
else:
 print "no match at beginning of string"
print

print "Searching"
mo1 = re.search('t.*n',str1)
if mo1:
 print mo1.group()
 print mo1.start()
 print mo1.end()
 print mo1.span()

print "Searching case insensitive"
mo1 = re.search('h.*n',str1,re.I)
if mo1:
 print mo1.group()
 print mo1.start()
 print mo1.end()
 print mo1.span()


print "findall"
re1 = re.compile('t')
lst1 = re1.findall(str1)
if lst1:
 print lst1
 for str2 in lst1:
  print str2
print


print "finditer"
re1 = re.compile('i.')
mol1 = re1.finditer(str1)
if mol1:
 for mo1 in mol1:
 	print mo1.group()
 	print mo1.start()
 	print mo1.end()
 	print mo1.span()
print