What Does the Percentage Sign Mean in Python

What does the percentage sign mean in Python

Modulus operator; gives the remainder of the left value divided by the right value. Like:

3 % 1 would equal zero (since 3 divides evenly by 1)

3 % 2 would equal 1 (since dividing 3 by 2 results in a remainder of 1).

What is the meaning of Percent sign in Python?

The '%' symbol has a lot of different meanings.

In this case, it's refererring to string formatting:
https://mkaz.com/2012/10/10/python-string-format/

Basically, it allows you to substitute a placeholder in the string with a new value.

>>> 'a%s' %('b')   # adding string
'ab'
>>> 'a%i' %(1)     # adding integer
'a1'
>>> 'a%d' %(1)     # adding integer (another form) 
'a1'

However, for integers, % has an entirely different meaning and can return a remainder from integer division (5%2 == 1).

What does % do to strings in Python?

It's the string formatting operator. Read up on string formatting in Python.

format % values

Creates a string where format specifies a format and values are the values to be filled in.

What does the double percent symbol do in Python?

This is not Python-specific. Whoever wrote that code is using the string "%%NOM%% as a placeholder, and using it to substitute the value of nom.

Is there an operator to calculate percentage in Python?

There is no such operator in Python, but it is trivial to implement on your own. In practice in computing, percentages are not nearly as useful as a modulo, so no language that I can think of implements one.

What does the double percentage sign (%%) mean?

The "Arithmetic operators" help page (which you can get to via ?"%%") says

‘%%’ indicates ‘x mod y’

which is only helpful if you've done enough programming to know that this is referring to the modulo operation, i.e. integer-divide x by y and return the remainder. This is useful in many, many, many applications. For example (from @GavinSimpson in comments), %% is useful if you are running a loop and want to print some kind of progress indicator to the screen every nth iteration (e.g. use if (i %% 10 == 0) { #do something} to do something every 10th iteration).

Since %% also works for floating-point numbers in R, I've just dug up an example where if (any(wts %% 1 != 0)) is used to test where any of the wts values are non-integer.

How can I selectively escape percent (%) in Python strings?

>>> test = "have it break."
>>> selectiveEscape = "Print percent %% in sentence and not %s" % test
>>> print selectiveEscape
Print percent % in sentence and not have it break.

How do I print a '%' sign using string formatting?

To print the % sign you need to 'escape' it with another % sign:

percent = 12
print "Percentage: %s %%\n" % percent  # Note the double % sign
>>> Percentage: 12 %

EDIT

Nowadays in python3 a better (and more readable) approach is to use f-strings. Note that other solutions (shown below) do work as well:

$python3
>>> percent = 12
>>> print(f'Percentage: {percent}%') # f-string
Percentage: 12%
>>> print('Percentage: {0}%'.format(percent)) # str format method
Percentage: 12%
>>> print('Percentage: %s%%' % percent) # older format, we 'escape' the '%' character
Percentage: 12%

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