Overview
A string is a list of characters in order.
A character is anything you can type on the keyboard in one keystroke,
like a letter, a number, or a backslash.
Strings can have spaces: "hello world".
An empty string is a string that has 0 characters.
Python strings are immutable
Python recognize as strings everything that is delimited by quotation marks
(" " or ' ').
String Manipulation
To manipulate strings, we can use some of Pythons built-in methods.
Creation
word = "Hello World" >>> print word Hello World
Accessing Use [ ] to access characters in a string
word = "Hello World" letter=word[0] >>> print letter H
Length
word = "Hello World" >>> len(word) 11
Finding
word = "Hello World"
>>> print word.count('l') # count how many times l is in the string
3
>>> print word.find("H") # find the word H in the string
0
>>> print word.index("World") # find the letters World in the string
6
Count
s = "Count, the number of spaces"
>>> print s.count(' ')
8
Slicing Use [ # : # ] to get set of letter Keep in mind that python, as many other languages, starts to count from 0!!
word = "Hello World" print word[0] #get one char of the word print word[0:1] #get one char of the word (same as above) print word[0:3] #get the first three char print word[:3] #get the first three char print word[-3:] #get the last three char print word[3:] #get all but the three first char print word[:-3] #get all but the three last character
word = "Hello World" word[start:end] # items start through end-1 word[start:] # items start through the rest of the list word[:end] # items from the beginning through end-1 word[:] # a copy of the whole list
Split Strings
word = "Hello World"
>>> word.split(' ') # Split on whitespace
['Hello', 'World']
Startswith / Endswith
word = "hello world"
>>> word.startswith("H")
True
>>> word.endswith("d")
True
>>> word.endswith("w")
False
Repeat Strings
print "."* 10 # prints ten dots >>> print "." * 10 ..........
Replacing
word = "Hello World"
>>> word.replace("Hello", "Goodbye")
'Goodbye World'
Changing Upper and Lower Case Strings
string = "Hello World" >>> print string.upper() HELLO WORLD >>> print string.lower() hello world >>> print string.title() Hello World >>> print string.capitalize() Hello world >>> print string.swapcase() hELLO wORLD
Reversing
string = "Hello World" >>> print ' '.join(reversed(string)) d l r o W o l l e H
Strip Python strings have the strip(), lstrip(), rstrip() methods for removing any character from both ends of a string. If the characters to be removed are not specified then white-space will be removed
word = "Hello World"
Strip off newline characters from end of the string
>>> print word.strip('
')
Hello World
strip() #removes from both ends
lstrip() #removes leading characters (Left-strip)
rstrip() #removes trailing characters (Right-strip)
>>> word = " xyz "
>>> print word
xyz
>>> print word.strip()
xyz
>>> print word.lstrip()
xyz
>>> print word.rstrip()
xyz
Concatenation To concatenate strings in Python use the "+" operator.
"Hello " + "World" # = "Hello World" "Hello " + "World" + "!"# = "Hello World!"
Join
>>> print ":".join(word) # #add a : between every char H:e:l:l:o: :W:o:r:l:d >>> print " ".join(word) # add a whitespace between every char H e l l o W o r l d
Testing A string in Python can be tested for truth value. The return type will be in Boolean value (True or False)
word = "Hello World"
word.isalnum() #check if all char are alphanumeric
word.isalpha() #check if all char in the string are alphabetic
word.isdigit() #test if string contains digits
word.istitle() #test if string contains title words
word.isupper() #test if string contains upper case
word.islower() #test if string contains lower case
word.isspace() #test if string contains spaces
word.endswith('d') #test if string endswith a d
word.startswith('H') #test if string startswith H
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