8.4 String formatting

2 min read•june 24, 2024

in Python offers powerful tools for creating dynamic text. From simple placeholders to precise numerical formatting, it allows for flexible and readable code. Understanding these techniques is crucial for effective string manipulation and presentation.

The method, alignment specifications, and precision controls provide fine-grained control over output. Mastering these concepts enables programmers to generate well-formatted strings for various applications, from user interfaces to data reporting.

String Formatting

String templates with format() method

Create string templates with placeholders for values inserted later using marked by curly braces
```
[{}](https://www.fiveableKeyTerm:{})
```
- Replacement fields can be empty
```
{}
```
  or contain a field name
```
{field_name}
```
Insert values into placeholders using the
```
format()
```
method
- Pass values as arguments to
```
format()
```
  in the order corresponding to the placeholders
- Use keyword arguments if field names are used in the replacement fields

Example:

"Hello, {}! My name is {}.".format("Alice", "Bob")

outputs "Hello, Alice! My name is Bob."

can also be achieved using ###-strings_0###, which are a more concise way to embed expressions inside

Alignment and width in string formatting

Control formatting of inserted values using alignment and width specifications inside replacement fields
Specify alignment using
```
[<](https://www.fiveableKeyTerm:<)
```
(left-align),
```
[^](https://www.fiveableKeyTerm:^)
```
(center-align), or
```
[>](https://www.fiveableKeyTerm:>)
```
(right-align) characters
- Default alignment is left-aligned
Specify width using an integer value representing the minimum number of characters the value should occupy
- Shorter values are padded with spaces, longer values are not truncated

Example:

"Left: {:<10} | Center: {[:^](https://www.fiveableKeyTerm::^)10} | Right: {[:>](https://www.fiveableKeyTerm::>)10}".format("Apple", "Banana", "Cherry")

outputs "Left: Apple | Center: Banana | Right: Cherry"

Numerical formatting with precision specifications

Specify precision and type for numerical values inside replacement fields
Specify precision using
```
[.n](https://www.fiveableKeyTerm:.n)
```
syntax, where
```
n
```
is the number of decimal places
- Floating-point numbers are rounded to the specified precision
- Precision has no effect on integers
Specify type using a type specifier character after the precision
- ```
f
```
  : Fixed-point notation (default for floating-point)
- ```
[e](https://www.fiveableKeyTerm:e)
```
  : Exponential notation
- ```
[g](https://www.fiveableKeyTerm:g)
```
  : General format (uses fixed-point for small numbers, exponential for large numbers)
- ```
[d](https://www.fiveableKeyTerm:d)
```
  : Decimal integer (default for integers)

Example:

"Fixed: {:.2f}, Exponential: {:.2e}, General: {:.2g}".format(3.14159)

outputs "Fixed: 3.14, Exponential: 3.14e+00, General: 3.1"

Additional Formatting Techniques

: An older method using
```
%
```
operator for string formatting
String literals can include to represent special characters or formatting
F-strings allow for direct embedding of expressions inside string literals, providing a more readable and concise syntax for string interpolation