Python Archives - Page 22 of 165

Python : How to Replace Single or Multiple Characters in a String ?

A string is a series of characters.

A character is nothing more than a representation of something. For example, the English language has 26 characters.
Computers do not work with characters, but rather with numbers (binary). Despite the fact that you see characters on your screen, they are internally stored and manipulated as a series of 0s and 1s.
Encoding is the process of converting a character to a number, and decoding is the reverse process. ASCII and Unicode are two of the most common encodings.
In Python, a string is a sequence of Unicode characters.. Unicode was created to include every character in all languages and to bring encoding uniformity. Python Unicode can teach you everything you need to know about Unicode.

Examples:

Input:

string="Hello this is BTechGeeks" oldstring='e' replacestring='q'

Output:

Hqllo this is BTqchGqqks

Replace Single or Multiple Characters in a String

There are several ways to replace single or multiple characters in a String of them are:

Replace all instances of a character or string in a string:
Replace the first n occurrences of a given character / substring in a string with another character / substring.
Replace multiple strings/characters in a string

Python has a string.replace() function

Syntax:

string.replace(old, new , count)

It returns a new string object that is a copy of the existing string with the content replaced. In addition, if count is not provided, it will return a string with all occurrences of ‘old’ replaced with ‘new’ string.
If the count parameter is supplied, it will return a string with the first ‘count’ occurrences of the ‘old’ string replaced with the ‘new’ string.

Replace all instances of a character or string in a string:

Assume we have a string, and now replace all occurrences of ‘e’ with ‘q’.

Below is the implementation:

# Function which replaces the string
def replaceMultipleString(string, oldstring, replacestring):
    # using replace
    resultstring = string.replace(oldstring, replacestring)

    # return the final string
    return resultstring


# Driver code
# given string
string = "Hello this is BTechGeeks"
# string which needs to be replaced
oldstring = 'e'
# replacing string/new string
replacestring = 'q'
# passing these strings to replaceMultipleString function
print(replaceMultipleString(string, oldstring, replacestring))

Output:

Hqllo this is BTqchGqqks

Because strings are immutable in Python, we can’t change their contents. As a result, member functions such as replace() produce a new string.

Replace the first n occurrences of a given character / substring in a string with another character / substring.

Suppose we want to replace character ‘e’ with ‘q000’ for first 2 i.e n occurrences then,

# Function which replaces the string
def replaceMultipleString(string, oldstring, replacestring):
    # using replace
    # providing count =2
    resultstring = string.replace(oldstring, replacestring, 2)

    # return the final string
    return resultstring


# Driver code
# given string
string = "Hello this is BTechGeeks"
# string which needs to be replaced
oldstring = 'e'
# replacing string/new string
replacestring = 'q000'
# passing these strings to replaceMultipleString function
print(replaceMultipleString(string, oldstring, replacestring))

Output:

Hq000llo this is BTq000chGeeks

Replace multiple strings/characters in a string

The string.replace() function can only replace occurrences of a single substring.

But what if we need to replace multiple substrings within the same string?

To replace all occurrences of these three characters ‘e’, ‘h’, and ‘i’ with the string ‘##’ let us write a new function that extends replace().

Below is the implementation:

# Function which replaces the string
def replaceMultipleString(string, oldstring, replacestring):
  # Traverse the old string which needs to be replaced
    for element in oldstring:
        # Check if string is in the original string
        if element in string:
            # Replace the string eith replacestring
            string = string.replace(element, replacestring)

    # return the final string
    return string


# Driver code
# given string
string = "Hello this is BTechGeeks"
# string which needs to be replaced
oldstring = ['e', 'i', 'h']
# replacing string/new string
replacestring = '##'
# passing these strings to replaceMultipleString function
print(replaceMultipleString(string, oldstring, replacestring))

Output:

H##llo t####s ##s BT##c##G####ks

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Python : How to access characters in string by index ?

Python / By Vikram Chiluka

A string is a collection of characters.

A character is simply a representation of something. The English language, for example, has 26 characters.
Computers work with numbers rather than characters (binary). Despite the fact that you see characters on your screen, they are stored and manipulated internally as a series of 0s and 1s.
The process of converting a character to a number is known as encoding, and the process of converting a number to a character is known as decoding. Two of the most common encodings are ASCII and Unicode.
A string in Python is a sequence of Unicode characters. Unicode was created in order to include every character in every language and to bring encoding uniformity. Python Unicode is capable of teaching you everything you need to know about Unicode.

Examples:

Input:

string="Hello this is BTechGeeks" index=3

Output:

Retrieve characters in string by index

In this article, we will look at how to access characters in a string using an index.

Accessing characters in a string by index | indexof
Using a negative index to access string elements
Using String Slicing :
Accessing Out Of range character in given string using Exceptional Handling:

>1)Accessing characters in a string by index | indexof

Python uses a zero-based indexing system for strings: the first character has index 0, the next has index 1, and so on.

The length of the string – 1 will be the index of the last character.

Suppose we want to access 3rd index in input string

We can implement it as:

# Given string
string = "Hello this is BtechGeeks"
# Given index
index = 3
character = string[index]
# printing the character at given index
print(character)

Output:

>2)Using a negative index to access string elements

Negative numbers may be used to specify string indices, in which case indexing is performed from the beginning of the string backward:

The last character is represented by string[-1]

The second-to-last character by string[-2], and so on.

If the length of the string is n, string[-n] returns the first character of the string.

Below is the implementation:

# Given string
string = "Hello this is BtechGeeks"
# given index from end
index = 3
# printing last two characters of string
print("Last character in the given string : ", string[-1])
print("Second Last character in given string : ", string[-2])
# printing n th character from end
print(str(index)+" character from end in given string :", string[-index])

Output:

Last character in the given string :  s
Second Last character in given string :  k
3 character from end in given string : e

>3)Using String Slicing :

# Given string
string = "Hello this is BtechGeeks"
# given start index and end index
startindex = 14
endindex = 19
# using slicing
print(string[startindex:endindex])

Output:

Btech

>4)Accessing Out Of range character in given string using Exceptional Handling:

IndexError will be thrown if an element in a string is accessed that is outside of its range, i.e. greater than its length. As a result, we should always check the size of an element before accessing it by index, i.e.

To handle the error we use exceptional handling in python

Below is the implementation:

# Given string
string = "Hello this is BtechGeeks"
# given index
index = 50
# using try and except
try:
    # if the given index is less than string length then it will print
    print(string[index])
# if index is out of range then it will print out of range
except:
    print("Index out of range")

Output:

Index out of range

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Python: Remove Last Element from a List

Python / By Vikram Chiluka

Lists are ordered sequences of objects that may contain a variety of different object types. Members of lists can also be duplicated. Lists in Python are similar to arrays in other programming languages.. However, there is one important distinction. Python lists can contain objects of different data types, while arrays can only contain elements of the same data type.

An index is a position in a list.

Given a list, the task is to remove last element from the given list.

Examples:

Input:

givenlist = ["Btech" , "Geeks" ,"is" ,"new" ,"online" ,"platform" ]

Output:

Btech Geeks is new online

Explanation:

platform is the last element in givenlist hence it is deleted.

Remove the final item from a list

There are several ways to remove the final item from the list some of them are:

Using pop() function
Using del keyword
Using slicing

Method #1:Using pop() function

The list class in Python has a function called pop(index), which takes an optional argument index and deletes the element at that index. If no justification is given, it deletes the last element of the list by default.

Below is the implementation:

# Function which removes last element
def removeLastElement(givenlist):
    # using pop() function
    givenlist.pop()
    # return the result list
    return givenlist


# Driver code
# given list
givenlist = ["Btech", "Geeks", "is", "new", "online", "platform"]


# passing list to remove last element
print(removeLastElement(givenlist))

Output:

['Btech', 'Geeks', 'is', 'new', 'online']

If the list is empty, the pop([i]) function throws an IndexError since it attempts to pop from an empty list.

Method #2:Using del keyword

The del statement is another way to delete an element from a list by using its index. It differs from the pop() function in that it does not return the element that has been removed. This does not generate a new list, unlike the slicing feature.

Below is the implementation:

# Function which removes last element
def removeLastElement(givenlist):
    # using del keyword
    del givenlist[-1]
    # return the result list
    return givenlist


# Driver code
# given list
givenlist = ["Btech", "Geeks", "is", "new", "online", "platform"]


# passing list to remove last element
print(removeLastElement(givenlist))

Output:

['Btech', 'Geeks', 'is', 'new', 'online']

If the list is empty, the above code raises an IndexError because it tries to reach an index of the list that is out of control.

Method #3: Using slicing

In Python, we know that lists can be cut. Slicing is a technique for removing the last element from a list. The aim is to create a sublist that contains all of the list’s elements except the last one. We must assign the new list to the original list since the slice operation returns a new list. The expression l = l[:-1], where l is your list, can be used to accomplish this. The abbreviation l[:-1] stands for l[0:len(l)-1].

Below is the implementation:

# Function which removes last element
def removeLastElement(givenlist):
    # using slicing
    givenlist = givenlist[:-1]
    # return the result list
    return givenlist


# Driver code
# given list
givenlist = ["Btech", "Geeks", "is", "new", "online", "platform"]


# passing list to remove last element
print(removeLastElement(givenlist))

Output:

['Btech', 'Geeks', 'is', 'new', 'online']

It should be noted that this function does not throw an error if the list is empty, but instead creates a copy of the list, which is not recommended.

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Python: Replace a Character in a String

Python / By Vikram Chiluka

A string is a character sequence.

A character is nothing more than a symbol. The English language, for example, has 26 characters.

Computers do not work with characters ,instead, they work with numbers (binary). Even though you see characters on your screen, they are stored and manipulated internally as a series of 0s and 1s.

The process of converting a character to a number is known as encoding, and the reverse process is known as decoding. Some of the most common encodings are ASCII and Unicode.

In Python, a string is a sequence of Unicode characters.. Unicode was created in order to include every character in all languages and bring encoding uniformity. Python Unicode can teach you about Unicode.

This article will go over various methods to replace a character in a string

Examples:

Input:

string="BTechGeeks" oldstring='e' replacestring='p'

Output:

BTpchGppks

Modifying a Character in a String

There are several ways to replace a character in a string some of them are:

Using replace() to replace all occurences
Using for loop
Using Regex

Method #1: Using replace() to replace all occurences

The Python string method replace() returns a copy of the string with old occurrences replaced with new, with the number of replacements optionally limited to max.

Syntax :

string .replace(old, new, count)

Parameters:

old−This is an old substring that needs to be replaced.
new − This is a new substring that will replace the old one.
max − Only the first count occurrences are replaced if the optional argument max is provided.

Return:
This method returns a string copy in which all occurrences of substring old are replaced with new. Only the first count occurrences are replaced if the optional argument max is provided.

Below is the implementation:

# Function which replaces the string
def replaceString(string, oldstring, replacestring):
    # Replace all occurrences of a character in string in python
    resultstring = string.replace(oldstring, replacestring)

    # return the final string
    return resultstring

# Driver code
# given string
string = "BTechGeeks"
# string which needs to be replaced
oldstring = 'e'
# replacing string/new string
replacestring = 'p'
# passing these strings to replaceString function
print(replaceString(string, oldstring, replacestring))

Output:

BTpchGppks

In this case, we passed the character to be replaced ‘e’ as the first argument and the character ‘p’ as the second. The replace() method then returned a copy of the original string by replacing all occurrences of the character’s’ with the character ‘X’.

Because strings are immutable in Python, we cannot change their contents. As a result, the replace() function returns a copy of the string containing the replaced content.

Replace only first two occurences of string:

Instead of replacing all occurrences of a character in a string, we can use the count argument in the replace() function to replace only the first few occurrences of a character in a string.

Below is the implementation:

# Function which replaces the string
def replaceString(string, oldstring, replacestring):
    # Replace first 2 occurrences of a character in string in python
    resultstring = string.replace(oldstring, replacestring, 2)

    # return the final string
    return resultstring


# Driver code
# given string
string = "BTechGeeks"
# string which needs to be replaced
oldstring = 'e'
# replacing string/new string
replacestring = 'p'
# passing these strings to replaceString function
print(replaceString(string, oldstring, replacestring))

Output:

BTpchGpeks

In this case, we passed the character to be replaced ‘e’ as the first argument and the character ‘p’ as the second. The third argument was then passed as 2. The third argument is optional and tells the replace() function how many occurrences of the given sub-string should be replaced.

The replace() method then returned a copy of the original string by replacing only the first two occurrences of ‘e’ with the symbol ‘p.’
Because strings are immutable in Python, we cannot change their contents. As a result, the replace() function returns a duplicate of the string with the replaced content.

Method #2:Using for loop

Create an empty string and then iterate through all of the characters in the original string. Add each character to the new string during iteration. However, if a character needs to be replaced, use the replacement character instead.

Below is the implementation:

# Function which replaces the string
def replaceString(string, oldstring, replacestring):
  # taking a empty string
    resultstring = ''
    # Traversee the originalstring
    for element in string:
      # if character is equal to old string then replace it
        if(element == oldstring):
            resultstring += replacestring
        else:
            resultstring += element

    # return the final string
    return resultstring


# Driver code
# given string
string = "BTechGeeks"
# string which needs to be replaced
oldstring = 'e'
# replacing string/new string
replacestring = 'p'
# passing these strings to replaceString function
print(replaceString(string, oldstring, replacestring))

Output:

BTpchGppks

It replaced all instances of the character ‘e’ with the letter ‘p’

Because strings are immutable in Python, we cannot change their contents. As a result, we made a new copy of the string that contained the replaced content.

Method #3:Using Regex

Python includes a regex module (re), which includes a function sub() for replacing the contents of a string based on patterns. We can use the re.sub() function to replace/substitute all occurrences of a character in a string.

Below is the implementation:

import re

# Function which replaces the string
def replaceString(string, oldstring, replacestring):
    # using regex
    resultstring = re.sub(oldstring, replacestring, string)

    # return the final string
    return resultstring


# Driver code
# given string
string = "BTechGeeks"
# string which needs to be replaced
oldstring = 'e'
# replacing string/new string
replacestring = 'p'
# passing these strings to replaceString function
print(replaceString(string, oldstring, replacestring))

Output:

BTpchGppks

In this case, we used the sub() function with the character to be replaced ‘e’ as the first argument and the character ‘p’ as the second argument. The third argument was then passed as the original string.

The Sub() function treated the first argument ‘s’ as a pattern and replaced all matches with the given replacement string, i.e ‘p’. As a result, it replaced all instances of the character ‘e’ with the character ‘p’ .Because strings are immutable in Python, we cannot change their contents. As a result, the regex module’s sub() function returns a copy of the string with the replaced content.
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Basics of Python – String Operations

Python / By Prasanna

In this Page, We are Providing Basics of Python – String Operations. Students can visit for more Detail and Explanation of Python Handwritten Notes Pdf.

Basics of Python – String Operations

String operations

Some of the string operations supported by Python are discussed below.

Concatenation

Strings can be concatenated using + operator.

>>> word=' Python '+' Program '
>>> word
' Python Program '

Two string literals next to each other are automatically concatenated; this only works with two literals, not with arbitrary string expressions.

>>> ' Python ' ' Program '
' Python Program ' 
>>> word1=' Python '
>>> word2=' Program '
>>> word1 word2
File "<stdin>", line 1
word1 word2
                   ∧
SyntaxError: invalid syntax

Repetition

Strings can be repeated with the * operator.

>>> word=' Help '
>>> word * 3
' Help Help Help '
>>> 3 * word
' Help Help Help '

Membership operation

As discussed previously, membership operators in and not in are used to test for membership in a sequence.

>>> word=' Python '
>>> 'th' in word
True
>>> ' T ' not in word
True

Slicing operation

The string can be indexed, the first character of a string has sub-script (index) as 0. There is no separate character type; a character is simply a string of size one. A sub-string can be specified with the slice notation.

>>> word=' Python'
>>> word [2]
' t '
>>> word [0:2]
' Py '

String slicing can be in form of steps, the operation s [ i : j : k ] slices the string s from i to j with step k.

>>> word [1 :6 : 2]
' yhn '

Slice indices have useful defaults, an omitted first index defaults to zero, an omitted second index defaults to the size of the string being sliced.

>>> word [ : 2]
' Py '
>>> word [2 : ]
' thon '

As mentioned earlier, the string is immutable, however, creating a new string with the combined content is easy and efficient.

>>> word [0] = ' J '
Traceback (most recent call last) :
File "<stdin>", line 1, in <module>
TypeError : 'str' object does not support item assignment
>>> 'J ' + word[ 1 : ]
' Jython '

If the upper bound is greater than the length of the string, then it is replaced by the string size; an upper bound smaller than the lower bound returns an empty string.

>>> word [ 2 : 50 ]
'thon '
>>> word [ 4 : 1 ]
' '

Indices can be negative numbers, which indicates counting from the right-hand side.

>>> word [ -1 ]
' n '
>>> word [ -2 ]
' o '
>>> word [ -3 : ] 
' hon '
>>> word [ : -3 ]
' Pyt ' 
>>> word[-0]     # -0 is same as 0
' P '

Out-of-range negative slice indices are truncated, but a single element (non-slice) index raises the IndexError exception.

>>> word [ -100 : ]
' Python '
>>> word [ -100 ]
Traceback (most recent call last) :
File "<stdin>", line 1, in <module>
IndexError : string index out of range

String formatting

String objects have an interesting built-in operator called modulo operator (%). This is also known as the “string formatting” or “interpolation operator”. Given format%values (where a format is a string object), the % conversion specifications in format are replaced with zero or more elements of values. The % character marks the start of the conversion specifier.

If the format requires a single argument, values may be a single non-tuple object. Otherwise, values must be a tuple with exactly the number of items specified by the format string, or a single mapping object (a dictionary). If the dictionary is provided, then the mapping key is provided in parenthesis.

>>> ' %s Python is a programming language. ' % ' Python '
' Python Python is a programming language. '
>>> ' %s Python is a programming language. ' % ( ' Python ' )
' Python Python is a programming language.'
>>>
>>> ' %s has %d quote types. ' % ( ' Python ' , 2 )
' Python has 2 quote types. '
>>> ' %s has %03d quote types. ' % ( ' Python ' , 2 )
' Python has 002 quote types. '  
>>> ' %( language )s has % ( number ) 03d quote types.' % \
. . . { " language " : " Python " , " number " : 2 }
' Python has 002 quote types. '

In the above example, 03 consists of two components:

0 is a conversion flag i.e. the conversion will be zero-padded for numeric values.
3 is minimum field width (optional).

Conversion	Meaning
D	Signed integer decimal.
1	Signed integer decimal.
E	Floating-point exponential format (lowercase).
E	Floating-point exponential format (uppercase).
F	Floating-point decimal format.
F	Floating-point decimal format.
g	Floating point format. Uses lowercase exponential format if the exponent is less than -4 or not less than precision, decimal format otherwise.
G	Floating point format. Uses uppercase exponential format if the exponent is less than -4 or not less than precision, decimal format otherwise.
s	String.

Precision (optional) is given as a dot (.) followed by the precision number. While using conversion type f, F, e, or E, the precision determines the number of digits after the decimal point, and it defaults to 6.

>>> " Today's stock price : %f " % 50
"Today's stock price: 50 000000"
>>> "Today's stock price : %F " % 50
"Today's stock price: 50 000000"
>>>
>>> "Today's stock price : %f " % 50.4625
"Today's stock price : 50 462500"
>>> "Today's stock price : %F " % 50.4625
"Today's stock price : 50 462500"
>>>
>>> "Today's stock price : %f " % 50.46251987624312359
"Today's stock price : 50. 462520"
>>> "Today's stock price : %F " % 50.46251987624312359
"Today's stock price : 50. 462520"
>>>
>>> "Today's stock price : %. 2f " % 50 . 4625
"Today's stock price : 50.46"
>>> "Today's stock price : %. 2F " % 50 . 4625
"Today's stock price : 50.46"
>>>
>>> "Today's stock price : %e " % 50 . 46251987624312359
"Today's stock price : 5 . 046252e+01 "
>>> "Today's stock price : %E " % 50 . 46251987624312359
"Today's stock price : 5 . 046252e+01 "
>>> "Today's stock price : % 3e " % 50 . 46251987624312359
"Today's stock price : 5 . 046e + 01 "
>>> "Today's stock price : % 3E " % 50 . 46251987624312359
"Today's stock price : 5 . 046E + 01 "

While using conversion type g or G, the precision determines the number of significant digits before and after the decimal point, and it defaults to 6.

>>> " Today's stock price : %g" % 50.46251987624312359
"Today's stock price: 50.4625"
>>> "Today's stock price: %G" % 50.46251987624312359
"Today's stock price: 50.4625"
>>>
>>> "Today's stock price: %g" % 0.0000005046251987624312359
"Today's stock price: 5.04625e-07"
»> "Today's stock price: %G" % 0.0000005046251987624312359
"Today's stock price: 5.04625E-07"

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Basics of Python – Regular Expression Module

Python / By Prasanna

In this Page, We are Providing Basics of Python – Regular Expression Module. Students can visit for more Detail and Explanation of Python Handwritten Notes Pdf.

Basics of Python – Regular Expression Module

Regular expression module

A regular expression (also called RE, or regex, or regex pattern) is a specialized approach in Python, using which programmers can specify rules for the set of possible strings that need to be matched; this set might contain English sentences, e-mail addresses, or anything. REs can also be used to modify a string or to split it apart in various ways.

Meta characters

Most letters and characters will simply match themselves. For example, the regular expression test will match the string test exactly. There are exceptions to this rule; some characters are special “meta characters”, and do not match themselves. Instead, they signal that some out-of-the-ordinary thing should be matched, or they affect other portions of the RE by repeating them or changing their meaning. Some of the meta characters are discussed below:

Meta character	Description	Example
[ ]	Used to match a set of characters.	[time] The regular expression would match any of the characters t, i, m, or e. [a-z] The regular expression would match only lowercase characters.
∧	Used to complement a set of characters.	[^∧time] The regular expression would match any other characters than t, i, m or e.
$	Used to match the end of string only.	time$ The regular expression would match time in ontime, but will not match time in timetable.
*	Used to specify that the previous character can be matched zero or more times.	tim*e The regular expression would match strings like timme, tie and so on.
+	Used to specify that the previous character can be matched one or more times.	tim+e The regular expression would match strings like timme, timmme, time and so on.
?	Used to specify that the previous character can be matched either once or zero times.	tim ?e The regular expression would only match strings like time or tie.
{ }	The curly brackets accept two integer values. The first value specifies the minimum number of occurrences and the second value specifies the maximum of occurrences.	tim{1,4}e The regular expression would match only strings time, timme, timmme or timmmme.

Regular expression module functions

Some of the methods of re module as discussed below:

re. compile ( pattern )
The function compile a regular expression pattern into a regular expression object, which can be used for matching using its match ( ) and search ( ) methods, discussed below.

>>> import re
>>> p=re.compile ( ' tim*e ' )

re. match ( pattern, string )
If zero or more characters at the beginning of the string match the regular expression pattern, match-( ) return a corresponding match object instance. The function returns None if the string does not match the pattern.

re. group ( )
The function return the string matched by the RE.

>>> m=re .match ( ' tim*e' , ' timme pass time ' )
>>> m. group ( )
' timme '