There are two ways to format strings in Python: Using F-strings (the preferred way since v3.6) and the format() method (older and less efficient).

To specify a string as an f-string, simply put an f in front of the string literal, like this: f”Hello World”.

txt = f"Hello World"
print(txt)

Output:

Hello World

To format values in an f-string, placeholders {} are added. A placeholder can contain variables, operations, functions, and modifiers to format the value.

name = "Johnny"
txt = f"My son's name is {name}."

print(txt)

Output:

My son's name is Johnny.

A placeholder can also include a modifier to format the value.

A modifier is included by adding a colon : followed by a legal formatting type, like .2f which means fixed point number with 2 decimals.

price = 99
txt = f"The price is ${price:.2f} dollars."

print(txt)

Output:

The price is $99.00 dollars.

This can also be done without using a variable. Just place the value within {}.

txt = f"The price is ${99:.2f} dollars."
print(txt)

Output:

The price is 99.00 dollars.

Do math operations:

txt = f"The price is ${10 * 29} dollars."
print(txt)

Output:

The price is $290 dollars.

Using if… else statements:

price = 99
txt = f"${price:.2f} is somewhat {'expensive' if price > 100 else 'affordable'}."

print(txt)

Output:

$99.00 is somewhat affordable.

Use the string method upper() to convert a value into upper case letters.

car = "maserati"
txt = f"I enjoy driving my {car.upper()}!"

print(txt)

Output:

I enjoy driving my MASERATI!

Custom functions can be created and used with f strings.

def myFunction(x):
    return x * 3.14

txt = f"Pie times 4 equals {myFunction(4)}."
print(txt)

Output:

Pie times 4 equals 12.56.

:<	Left aligns the result (within the available space)
:>	Right aligns the result (within the available space)
:^	Center aligns the result (within the available space)
:=	Places the sign to the left most position
:+	Use a plus sign to indicate if the result is positive or negative
:-	Use a minus sign for negative values only
:	Use a space to insert an extra space before positive numbers (and a minus sign before negative numbers)
:,	Use a comma as a thousand separator
:_	Use a underscore as a thousand separator
:b	Binary format
:c	Converts the value into the corresponding Unicode character
:d	Decimal format
:e	Scientific format, with a lower case e
:E	Scientific format, with an upper case E
:f	Fix point number format
:F	Fix point number format, in uppercase format (show inf and nan as INF and NAN)
:g	General format
:G	General format (using a upper case E for scientific notations)
:o	Octal format
:x	Hex format, lower case
:X	Hex format, upper case
:n	Number format
:%	Percentage format

The format() method can still be used, but f-strings are faster and the preferred way to format strings.

name = "Johnny"
txt = "My son's name is {}."

print(txt.format(name))

Output:

My son's name is Johnny.

Parameters can be used inside curly brackets to specify how to convert a value.

price = 99
txt = "The price is ${:.2f} dollars."

print(txt.format(price))

Output:

The price is $99.00 dollars.

Using multiple parameters:

quantity = 16
item = 41101
price = 99
order = "We need {} pieces of item {} which cost ${:.2f} each."

print(order.format(quantity, item, price))

Output:

We need 16 pieces of item 41101 which cost $99.00 each.

Index numbers (a number inside the curly brackets) can be used to ensure the values are placed in the correct placeholders. This is similar to creating/using an array.

quantity = 16
item = 41101
price = 99
order = "We need {0} pieces of item {1} which cost ${2:.2f} each."

print(order.format(quantity, item, price))

Output:

We need 16 pieces of item 41101 which cost $99.00 each.

Index numbers can also be used when referring to the same value more than once.

age = 12
name = "Johnny"
txt = "My son's name is {1}. {1} is {0} years old."

print(txt.format(age, name))

Output:

My son's name is Johnny. Johnny is 12 years old.

Named indexes can be used by entering a name inside the curly brackets {carname}. Then when passing a parameter, the value is also passed in the format (carname = “Maserati”).

mycar = "I drive a {carname} {carmodel}."
print(mycar.format(carname = "Maserati", carmodel = "Quattroporte"))

Output:

I drive a Maserati Quattroporte.

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