Format

This is a built-in function. With it, we take a value (like an integer or a string) and apply formatting to it. We receive the formatted string.

Typically in Python, we can use string-based methods instead of format. But sometimes the format() built-in is needed (like for adding commas to numbers).

An example

Here is an example of the format method. First the number 1000 is formatted as "1,000" by using a comma as the format string.

Detail A ":" character is applied as padding. The "greater than" character, followed by 10s, means right-align in a string of length 10.

# Format this number with a comma.
result = format(1000, ",")
print(result)

# Align to the right of 10 chars, filling with ":" and as a string.
result = format("cat", ":>10s")
print(result)1,000
:::::::cat

`String` format

There is a format() method on strings. This is different from that format() built-in. Here we insert values into substitutions in a format string.

Detail The "{number}" pattern in the string has the "cat_number" inserted into it. The same thing happens with "color."

Tip We assign names to variables in the argument list of format(). The variables are bound to names in this way.

cat_color = "orange"
cat_number = 10

# Use format method on string.
# ... Assign variables to names in pattern.
result = "cat {number} is {color}".format(number=cat_number, color=cat_color)
print(result)
cat 10 is orange

Format literal, f

We can prefix a string literal with the "f" character to have a format literal. Inside curly brackets, variables are substituted directly into the format string.

Here The dog_size and dog_color variables are placed inside the format string.

dog_color = "orange"
dog_size = 100

# Use format literal.
result = f"the dog weighs {dog_size} and is {dog_color}"
print(result)
the dog weighs 100 and is orange

Padding

For padding, consider the ljust and rjust methods. This can make programs simpler over using a complex (hard-to-remember) format string.

Format, some notes

Format strings are sometimes complex. Consider adding a def that surrounds the call to format with the complex format string. Then just call that method.

A review

It is possible to format strings with the format() built-in. We can add padding. We can add commas to the string representations of numbers.