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Confused by {} in Python code - Oliver - Dec-03-2017
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))))
---
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
RE: Confused by {} in Python code - Larz60+ - Dec-03-2017
In your code snippet, The {} is a placeholder for formatted text, see: https://docs.python.org/3/tutorial/inputoutput.html
you will also see '{' and '}' as bounds for creating a dictionary.
RE: Confused by {} in Python code - j.crater - Dec-03-2017
It is a way to format strings in Python. Similar to using % notation in Python 2, C language etc. So in your case {} gets substituted with value of M, which is calculated with the formula you provided.
Here you can find documentation on it and a few simple examples:
https://docs.python.org/3.4/library/string.html#format-examples
RE: Confused by {} in Python code - sparkz_alot - Dec-03-2017
In version 3.6.3 you can also use:
print(f"M = {M}")
RE: Confused by {} in Python code - snippsat - Dec-03-2017
It's called string formatting.
The evolution of string formatting.
>>> M = 100
>>> # old don't use
>>> print('M = %d' % M)
M = 100
>>>
>>> # Python 2.6 we get format()
>>> print('M = {}'.format(M))
M = 100
>>>
>>> # Python 3.6 we get f-string
>>> print(f'M = {M}')
M = 100f-string is the future,but format() will be used for a long time.f-string can take expressions here calculate and upper():
>>> a = 10
>>> b = 20
>>> s = 'correct'
>>> print(f'The sum of a {a} and b {b} is {a+b} {s.upper()}')
The sum of a 10 and b 20 is 30 CORRECTMore about format() PyForamt.
RE: Confused by {} in Python code - j.crater - Dec-03-2017
(Dec-03-2017, 04:11 PM)snippsat Wrote: More about format() PyFormat.
Nice answer and awesome resource, thanks!
RE: Confused by {} in Python code - Oliver - Dec-03-2017
(Dec-03-2017, 04:06 PM)j.crater Wrote: It is a way to format strings in Python. Similar to using % notation in Python 2, C language etc. So in your case {} gets substituted with value of M, which is calculated with the formula you provided.
Here you can find documentation on it and a few simple examples:
https://docs.python.org/3.4/library/string.html#format-examples
Thanks very much!
That was exactly what I needed.
Sorry, I should have RTFM first. :)
- O
(Dec-03-2017, 04:11 PM)snippsat Wrote: It's called string formatting.
The evolution of string formatting.
>>> M = 100 >>> # old don't use >>> print('M = %d' % M) M = 100 >>> >>> # Python 2.6 we get format() >>> print('M = {}'.format(M)) M = 100 >>> >>> # Python 3.6 we get f-string >>> print(f'M = {M}') M = 100f-string is the future,but format() will be used for a long time.
f-string can take expressions here calculate and upper():
>>> a = 10 >>> b = 20 >>> s = 'correct' >>> print(f'The sum of a {a} and b {b} is {a+b} {s.upper()}') The sum of a 10 and b 20 is 30 CORRECTMore about format() PyForamt.
Excellent! I've copied these for reference.
- O