should i check if a substring exists before trying to replace it?

In python3, is it worth checking if a substring exists before attempting to replace it? I'm checking about 40,000 strings and only expect to find substring1 in about 1% of them. Does it take longer to check and skip or to try and fail to replace?

if substring1 in string:
   string = string.replace(substring1, substring2)

or just

string = string.replace(substring1, substring2)

Suggestion : 2

Last Updated : 09 Aug, 2022

Given two strings, check if a substring is there in the given string or not.

Example 1: Input: Substring = "geeks"
String = "geeks for geeks"
Output: yes
Example 2: Input: Substring = "geek"
String = "geeks for geeks"
Output: yes

Yes!it is present in the string

Output:

Yes!it is present in the string

yes

YES

NO

Suggestion : 3

Returns a new string in which all occurrences of a specified string in the current instance are replaced with another specified string, using the provided comparison type.,Returns a new string in which all occurrences of a specified string in the current instance are replaced with another specified string.,Returns a new string in which all occurrences of a specified string in the current instance are replaced with another specified string, using the provided culture and case sensitivity.,Returns a new string in which all occurrences of a specified Unicode character or String in the current string are replaced with another specified Unicode character or String.

1._

public:
   System::String ^ Replace(char oldChar, char newChar);

public:
 System::String ^ Replace(char oldChar, char newChar);

public string Replace(char oldChar, char newChar);

public string Replace (char oldChar, char newChar);

member this.Replace: char * char - > string

The following example creates a comma separated value list by substituting commas for the blanks between a series of numbers.

using namespace System;
int main() {
   String ^ str = "1 2 3 4 5 6 7 8 9";
   Console::WriteLine("Original string: \"{0}\"", str);
   Console::WriteLine("CSV string:      \"{0}\"", str - > Replace(' ', ','));
}

//
// This example produces the following output:
// Original string: "1 2 3 4 5 6 7 8 9"
// CSV string:      "1,2,3,4,5,6,7,8,9"
//

String str = "1 2 3 4 5 6 7 8 9";
Console.WriteLine("Original string: \"{0}\"", str);
Console.WriteLine("CSV string:      \"{0}\"", str.Replace(' ', ','));

// This example produces the following output:
// Original string: "1 2 3 4 5 6 7 8 9"
// CSV string:      "1,2,3,4,5,6,7,8,9"

1._

public:
   System::String ^ Replace(System::String ^ oldValue, System::String ^ newValue);

public:
 System::String ^ Replace(System::String ^ oldValue, System::String ^ newValue);

public string Replace(string oldValue, string newValue);

public string Replace (string oldValue, string newValue);

public string Replace(string oldValue, string ? newValue);

member this.Replace : string * string -> string

Public Function Replace(oldValue As String, newValue As String) As String

The following example demonstrates how you can use the Replace method to correct a spelling error.

using namespace System;
int main() {
   String ^ errString = "This docment uses 3 other docments to docment the docmentation";
   Console::WriteLine("The original string is:\n'{0}'\n", errString);

   // Correct the spelling of S"document".
   String ^ correctString = errString - > Replace("docment", "document");
   Console::WriteLine("After correcting the string, the result is:\n'{0}'", correctString);
}
//
// This code example produces the following output:
//
// The original string is:
// 'This docment uses 3 other docments to docment the docmentation'
//
// After correcting the string, the result is:
// 'This document uses 3 other documents to document the documentation'
//

1._

public:
   System::String ^ Replace(System::String ^ oldValue, System::String ^ newValue, StringComparison comparisonType);

public:
 System::String ^ Replace(System::String ^ oldValue, System::String ^ newValue, StringComparison comparisonType);

public string Replace(string oldValue, string ? newValue, StringComparison comparisonType);

public string Replace (string oldValue, string? newValue, StringComparison comparisonType);

public string Replace(string oldValue, string newValue, StringComparison comparisonType);

member this.Replace : string * string * StringComparison -> string

Public Function Replace(oldValue As String, newValue As String, comparisonType As StringComparison) As String

Because this method returns the modified string, you can chain together successive calls to the Replace method to perform multiple replacements on the original string. Method calls are executed from left to right. The following example provides an illustration.

String s = "aaa";
Console.WriteLine("The initial string: '{0}'", s);
s = s.Replace("a", "b").Replace("b", "c").Replace("c", "d");
Console.WriteLine("The final string: '{0}'", s);

// The example displays the following output:
//       The initial string: 'aaa'
//       The final string: 'ddd'

1._

public:
   System::String ^ Replace(System::String ^ oldValue, System::String ^ newValue, bool ignoreCase, System::Globalization::CultureInfo ^ culture);

public:
 System::String ^ Replace(System::String ^ oldValue, System::String ^ newValue, bool ignoreCase, System::Globalization::CultureInfo ^ culture);

public string Replace(string oldValue, string ? newValue, bool ignoreCase, System.Globalization.CultureInfo ? culture);

public string Replace (string oldValue, string? newValue, bool ignoreCase, System.Globalization.CultureInfo? culture);

public string Replace(string oldValue, string newValue, bool ignoreCase, System.Globalization.CultureInfo culture);

member this.Replace : string * string * bool * System.Globalization.CultureInfo -> string

Public Function Replace(oldValue As String, newValue As String, ignoreCase As Boolean, culture As CultureInfo) As String

String s = "aaa";
Console.WriteLine("The initial string: '{0}'", s);
s = s.Replace("a", "b").Replace("b", "c").Replace("c", "d");
Console.WriteLine("The final string: '{0}'", s);

// The example displays the following output:
//       The initial string: 'aaa'
//       The final string: 'ddd'

Suggestion : 4

Last modified: Aug 15, 2022, by MDN contributors

replace(pattern, replacement)

"xxx".replace("", "_"); // "_xxx"

"foo".replace(/(f)/, "$2"); // "$2oo"; the regex doesn't have the second group
"foo".replace("f", "$1"); // "$1oo"
"foo".replace(/(f)|(g)/, "$2"); // "oo"; the second group exists but isn't matched

function replacer(match, p1, p2, /* …, */ pN, offset, string, groups) {
   return replacement;
}

function replacer(match, p1, p2, p3, offset, string) {
   // p1 is non-digits, p2 digits, and p3 non-alphanumerics
   return [p1, p2, p3].join(' - ');
}
const newString = 'abc12345#$*%'.replace(/([^\d]*)(\d*)([^\w]*)/, replacer);
console.log(newString); // abc - 12345 - #$*%

const str = 'Twas the night before Xmas...';
const newstr = str.replace(/xmas/i, 'Christmas');
console.log(newstr); // Twas the night before Christmas...

Suggestion : 5

Remote Work 2022 , Remote Work 2022

Syntax of in:

substring in string

Code to check if python string contains a substring:

if "Hire" in "Hire the top freelancers":
print("Exists")
else:
   print("Does not exist")

#Output - Exists

This method converts the string to lower case. As strings are immutable, this would not affect the original string.

if "hire" in "Hire the top freelancers".lower():
   print("Exists")
else:
   print("Does not exist")

#Output - Exists

Code using index():

try:
"Hire the top freelancers".index("Hire")
except ValueError:
   print("Does not exist")
else:
   print(sting.index(sti))

#Output = 0

index() is case sensitive, ensure you use the .lower() function to avoid bugs.

try:
"Hire the top freelancers".lower().index("hire")
except ValueError:
   print("Does not exist")
else:
   print(sting.index(sti))

#Output = 0

Suggestion : 6

To replace all occurrences of a substring in a string with a new one, you must use a regular expression.,Use a regular expression with the global flag (g) to replace all occurrences of a substring with a new one.,Use the replace() method to return a new string with a substring replaced by a new one.,Summary: in this tutorial, you’ll how to use JavaScript String replace() method to replace a substring in a string with a new one.

The following shows the syntax of the replace() method:

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let newStr = str.replace(substr, newSubstr);
Code language: JavaScript(javascript)

The following example uses the replace() to replace the JS in the string 'JS will, JS will rock you' wit the new substring JavaScript:

let str = 'JS will, JS will rock you!';
let newStr = str.replace('JS', 'JavaScript');

console.log(newStr);
Code language: JavaScript(javascript)

Output:

JavaScript will, JS will rock you!Code language: JavaScript(javascript)

The following example uses the global flag (g) to replace all occurrences of the JS in the str by the JavaScript:

let str = 'JS will, JS will rock you!';
let newStr = str.replace(/JS/g, 'JavaScript');

console.log(newStr);
Code language: JavaScript(javascript)

If you want to ignore cases for searching and replacement, you can use the ignore flag (i) in the regular expression like this:

let str = 'JS will, Js will rock you!';
let newStr = str.replace(/JS/gi, 'JavaScript');

console.log(newStr);
Code language: JavaScript(javascript)