Confused by {} in Python code

[Oliver]

I downloaded some Python code that has a line of code like this:

print('M = {}'.format(M))

where M is defined like this:

M = ((n - m) * np.log(np.linalg.det(Xp))) \
- (n_1 - 1) * (np.log(np.linalg.det(np.cov(X0)))) - (n_2 - 1) * (np.log(np.linalg.det(np.cov(X1))))

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I'm confused what's going on with the "{}" inside the 'M = {}'.

What do the braces represent/do in this context?

Thanks very much in advance,

-O