Monday, June 22, 2020

Python Strings Tutorial



Hello guys! Welcome back to another section of my tutorial on Python. In this tutorial guide, we are going to be discussing about Python String.

Strings are among the most popular data types on Python. They can be created by enclosing of characters in quotes. Python treats single quotes the same way as it treats double quotes. Creating a string is as simple as assigning value to a variable.

Example

Following below is a simple example -

var1 = 'Hello World!'
var2 = "Python Programming"

Accessing Values in Strings

Python does not support a character type; these are treated as strings of the length 1, thus also considered as substring.

To access substrings, you should make use of the square brackets for slicing, along with index or indices  to obtain your substring.

Example

Following below is a simple example -

#!/usr/bin/python

var1 = 'Hello World!'
var2 = "Python Programming"

print "var1[0]: ", var1[0]
print "var2[1:5]: ", var2[1:5]

Output

Below is the output of the above example -

var1[0]:  H
var2[1:5]:  ytho


Updating Strings in Python

You can update an existing Python string by re-assigning a variable to another string. The new value can be related to its previous value or to a completely different string altogether.

Example

Following below is a simple example -

#!/usr/bin/python

var1 = 'Hello World!'
print "Updated String :- ", var1[:6] + 'Python'

Output

Below is the output of the above example -

Updated String :-  Hello Python

Escape Characters

The following table is a list of escape characters that can be constituted with backslash notation in Python.

An escape character gets interpreted in a single quoted as well as a double quoted strings.

Backslash notationHexadecimal characterDescription
\a0x07Bell or alert
\b0x08Backspace
\cxControl-x
\C-xControl-x
\e0x1bEscape
\f0x0cFormfeed
\M-\C-xMeta-Control-x
\n0x0aNewline
\nnnOctal notation, where n is in the range 0.7
\r0x0dCarriage return
\s0x20Space
\t0x09Tab
\v0x0bVertical tab
\xCharacter x
\xnnHexadecimal notation, where n is in the range 0.9, a.f, or A.F

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String Special Operators

Assuming that string variable a holds 'Hello' and variable b holds 'Python', then -

OperatorDescriptionExample
+Concatenation - Adds values on either side of the operatora + b will give HelloPython
*Repetition - Creates new strings, concatenating multiple copies of the same stringa*2 will give -HelloHello
[]Slice - Gives the character from the given indexa[1] will give e
[ : ]Range Slice - Gives the characters from the given rangea[1:4] will give ell
inMembership - Returns true if a character exists in the given stringH in a will give 1
not inMembership - Returns true if a character does not exist in the given stringM not in a will give 1
r/RRaw String - Suppresses actual meaning of Escape characters. The syntax for raw strings is exactly the same as for normal strings with the exception of the raw string operator, the letter "r," which precedes the quotation marks. The "r" can be lowercase (r) or uppercase (R) and must be placed immediately preceding the first quote mark.print r'\n' prints \n and print R'\n'prints \n
%Format - Performs String formattingSee at next section

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String Formatting Operator

String format operator is one the Python's best features. This operator is unique to strings and makes up for the pack of having functions from the C's printf() family.

Example

The following below is a simple example -

#!/usr/bin/python

print "My name is %s and weight is %d kg!" % ('Kennedy', 29)

Output

Below is the output of the above example -

My name is Kennedy and weight is 29 kg!

Below is the list of the complete set of symbols which can be used along with the string format operator % -

Format SymbolConversion
%ccharacter
%sstring conversion via str() prior to formatting
%isigned decimal integer
%dsigned decimal integer
%uunsigned decimal integer
%ooctal integer
%xhexadecimal integer (lowercase letters)
%Xhexadecimal integer (UPPERcase letters)
%eexponential notation (with lowercase 'e')
%Eexponential notation (with UPPERcase 'E')
%ffloating point real number
%gthe shorter of %f and %e
%Gthe shorter of %f and %E


Other supported functionality, and symbols are listed in the following table below -

SymbolFunctionality
*argument specifies width or precision
-left justification
+display the sign
<sp>leave a blank space before a positive number
#add the octal leading zero ( '0' ) or hexadecimal leading '0x' or '0X', depending on whether 'x' or 'X' were used.
0pad from left with zeros (instead of spaces)
%'%%' leaves you with a single literal '%'
(var)mapping variable (dictionary arguments)
m.n.m is the minimum total width and n is the number of digits to display after the decimal point (if appl.)

Triple Quotes

The Python's triple quotes comes to the rescue by allowing strings to span multiple lines, which includes verbatim NEWLINEs, TABs, and as well other special characters.

The syntax for the Python triple quotes consists of three consecutive single or double quotes.

#!/usr/bin/python

para_str = """this is a long string that is made up of
several lines and non-printable characters such as
TAB ( \t ) and they will show up that way when displayed.
NEWLINEs within the string, whether explicitly given like
this within the brackets [ \n ], or just a NEWLINE within
the variable assignment will also show up.
"""
print para_str

Output

When the above code is executed, it produces the following result. Note - how all single special characters has been converted to its printable form right down to the last NEWLINE at the end of the string between the "up." and closing triple quotes. Also note that NEWLINEs occur either with an explicit carriage return at the end of a line or its escape code (\n) -

this is a long string that is made up of
several lines and non-printable characters such as
TAB (    ) and they will show up that way when displayed.
NEWLINEs within the string, whether explicitly given like
this within the brackets [
 ], or just a NEWLINE within
the variable assignment will also show up.


Raw strings do not treat backslash as a special character. Every character which you put into a raw string stays exactly the same way you wrote it.

Example

Below is a very simple example -

#!/usr/bin/python

print 'C:\\nowhere'

Output

Below is the output of the above example -

C:\nowhere

Now let's make use of raw string. We would put expression in r'expression' as follows -

#!/usr/bin/python

print r'C:\\nowhere'

When the above code is executed, it produces the following output -

C:\\nowhere

Unicode String
Normally strings in Python are stored internally as an 8-bit ASCII, while Unicode strings are stored as a 16-bit Unicode. This allows a more varied set of characters, including special characters from most languages in the world.

Example
The following below is a very short example -

#!/usr/bin/python

print u'Hello, world!'

Output
Below is the output of the above example -

Hello, world!



Built-in String Methods
Python includes the following built-in methods for manipulation of strings -

Sr.No.Methods with Description
1capitalize()
Capitalizes first letter of string
2center(width, fillchar)
Returns a space-padded string with the original string centered to a total of width columns.
3count(str, beg= 0,end=len(string))
Counts how many times str occurs in string or in a substring of string if starting index beg and ending index end are given.
4decode(encoding='UTF-8',errors='strict')
Decodes the string using the codec registered for encoding. encoding defaults to the default string encoding.
5encode(encoding='UTF-8',errors='strict')
Returns encoded string version of string; on error, default is to raise a ValueError unless errors is given with 'ignore' or 'replace'.
6endswith(suffix, beg=0, end=len(string))
Determines if string or a substring of string (if starting index beg and ending index end are given) ends with suffix; returns true if so and false otherwise.
7expandtabs(tabsize=8)
Expands tabs in string to multiple spaces; defaults to 8 spaces per tab if tabsize not provided.
8find(str, beg=0 end=len(string))
Determine if str occurs in string or in a substring of string if starting index beg and ending index end are given returns index if found and -1 otherwise.
9index(str, beg=0, end=len(string))
Same as find(), but raises an exception if str not found.
10isalnum()
Returns true if string has at least 1 character and all characters are alphanumeric and false otherwise.
11isalpha()
Returns true if string has at least 1 character and all characters are alphabetic and false otherwise.
12isdigit()
Returns true if string contains only digits and false otherwise.
13islower()
Returns true if string has at least 1 cased character and all cased characters are in lowercase and false otherwise.
14isnumeric()
Returns true if a unicode string contains only numeric characters and false otherwise.
15isspace()
Returns true if string contains only whitespace characters and false otherwise.
16istitle()
Returns true if string is properly "titlecased" and false otherwise.
17isupper()
Returns true if string has at least one cased character and all cased characters are in uppercase and false otherwise.
18join(seq)
Merges (concatenates) the string representations of elements in sequence seq into a string, with separator string.
19len(string)
Returns the length of the string
20ljust(width[, fillchar])
Returns a space-padded string with the original string left-justified to a total of width columns.
21lower()
Converts all uppercase letters in string to lowercase.
22lstrip()
Removes all leading whitespace in string.
23maketrans()
Returns a translation table to be used in translate function.
24max(str)
Returns the max alphabetical character from the string str.
25min(str)
Returns the min alphabetical character from the string str.
26replace(old, new [, max])
Replaces all occurrences of old in string with new or at most max occurrences if max given.
27rfind(str, beg=0,end=len(string))
Same as find(), but search backwards in string.
28rindex( str, beg=0, end=len(string))
Same as index(), but search backwards in string.
29rjust(width,[, fillchar])
Returns a space-padded string with the original string right-justified to a total of width columns.
30rstrip()
Removes all trailing whitespace of string.
31split(str="", num=string.count(str))
Splits string according to delimiter str (space if not provided) and returns list of substrings; split into at most num substrings if given.
32splitlines( num=string.count('\n'))
Splits string at all (or num) NEWLINEs and returns a list of each line with NEWLINEs removed.
33startswith(str, beg=0,end=len(string))
Determines if string or a substring of string (if starting index beg and ending index end are given) starts with substring str; returns true if so and false otherwise.
34strip([chars])
Performs both lstrip() and rstrip() on string.
35swapcase()
Inverts case for all letters in string.
36title()
Returns "titlecased" version of string, that is, all words begin with uppercase and the rest are lowercase.
37translate(table, deletechars="")
Translates string according to translation table str(256 chars), removing those in the del string.
38upper()
Converts lowercase letters in string to uppercase.
39zfill (width)
Returns original string leftpadded with zeros to a total of width characters; intended for numbers, zfill() retains any sign given (less one zero).
40isdecimal()
Returns true if a unicode string contains only decimal characters and false otherwise.

In our subsequent tutorials, we are going to be discussing the above listed methods one after the other.


Alright guys! This is where we are rounding up for this tutorial post. In my next tutorial, we are going to be discussing about the Python String capitalize() method.

Feel free to ask your questions where necessary and i will attend to them as soon as possible. If this tutorial was helpful to you, you can use the share button to share this tutorial.

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Thanks for reading and bye for now.
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