How to Put a Variable'S Value Inside a String

How do I put a variable’s value inside a string?

plot.savefig('hanning(%d).pdf' % num)

The % operator, when following a string, allows you to insert values into that string via format codes (the %d in this case). For more details, see the Python documentation:

printf-style String Formatting

How to interpolate variables in strings in JavaScript, without concatenation?

You can take advantage of Template Literals and use this syntax:

`String text ${expression}`

Template literals are enclosed by the back-tick (` `) (grave accent) instead of double or single quotes.

This feature has been introduced in ES2015 (ES6).

Example

var a = 5;
var b = 10;
console.log(`Fifteen is ${a + b}.`);
// "Fifteen is 15.

How neat is that?

Bonus:

It also allows for multi-line strings in javascript without escaping, which is great for templates:

return `
    <div class="${foo}">
         ...
    </div>
`;

Browser support:

As this syntax is not supported by older browsers (mostly Internet Explorer), you may want to use Babel/Webpack to transpile your code into ES5 to ensure it will run everywhere.

Side note:

Starting from IE8+ you can use basic string formatting inside console.log:

console.log('%s is %d.', 'Fifteen', 15);
// Fifteen is 15.

How to insert a variable value in a string in python

Use string formatting:

s = "Your first value is {} your second value is {}".format(amount1, amount2)

This will automatically handle the data type conversion, so there is no need for str().

Consult the Python docs for detailed information:

https://docs.python.org/3.6/library/string.html#formatstrings

Putting a variable into a string (quote)

You should use a string formatter here, or concatenation. For concatenation you'll have to convert an int to a string. You can't concatenate ints and strings together.

This will raise the following error should you try:

TypeError: unsupported operand type(s) for +: 'int' and 'str'

Formatting:

quote = "You are %d years old" % age
quote = "You are {} years old".format(age)

Concatenation (one way)

quote = "You are " + str(age) + " years old" 

Edit: As noted by J.F. Sebastian in the comment(s) we can also do the following

In Python 3.6:

f"You are {age} years old"

Earlier versions of Python:

"You are {age} years old".format(**vars())

R variable inside a string

variable2 <- paste0("I am argument:",variable1,"text continue")

Insert variable values in the middle of a string

You can use string.Format:

string template = "Hi We have these flights for you: {0}. Which one do you want";
string data = "A, B, C, D";
string message = string.Format(template, data);

You should load template from your resource file and data is your runtime values.

Be careful if you're translating to multiple languages, though: in some cases, you'll need different tokens (the {0}) in different languages.

How an I insert variables at a specific place in a string?

You can use ES2015 template literals. But, the variables should be defined before using them.

var name1 = "Phil";var name2 = "Amy";var templateString = `Hello ${name1}, my name is ${name2}`;
console.log(templateString);document.body.innerHTML = templateString;