CODEWITHSUNDEEP
python
noobie
noobie

Reputation: 67

What do empty curly braces mean in a string?

So I have been browsing through online sites to read a file line by line and I come to this part of this code:

print("Line {}: {}".format(linecount, line))

I am quite confused as to what is happening here. I know that it is printing something, but it shows:

"Line{}"

I do not understand what this means. I know that you could write this:

foo = "hi"
print(f"{foo} bob")

But I don't get why there are empty brackets.

Upvotes: 4

Views: 3981

Answers (3)

dawg
dawg

Reputation: 103764

Empty braces are equivalent to numeric braces numbered from 0:

>>> '{}: {}'.format(1,2)
'1: 2'
>>> '{0}: {1}'.format(1,2)
'1: 2'

Just a shortcut.

But if you use numerals you can control the order:

>>> '{1}: {0}'.format(1,2)
'2: 1'

Or the number of times something is used:

>>> '{0}: {0}, {1}: {1}'.format(1,2)
'1: 1, 2: 2'

Which you cannot do with empty braces.

Upvotes: 4

Zack Plauché
Zack Plauché

Reputation: 4200

Doing "My {} string is {}".format('formatted', 'awesome') just fills in the curly braces with the args you provide in the format function in the order you enter the arguments.

So the first {} in the above string would get 'formatted' and the second in that case would get 'awesome'.

It's an older version of formatting strings than f strings (which I'm glad I started learning Python when these already came out), but you can equally write something like this similar to f-strings:

>>> template = 'I love {item}. It makes me {emotion}'
>>>
>>> my_sentence = template.format(item='fire', emotion='calm')
>>> print(my_sentence)
I love fire. It makes me calm.

Upvotes: 2

Victor Alessander
Victor Alessander

Reputation: 172

This is a different way to interpolate strings in Python.

Docs: https://docs.python.org/3/tutorial/inputoutput.html#fancier-output-formatting

The usage of string interpolations like this f'Results of the {year} {event}' came in Python 3.6.

Upvotes: 1

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