What does the percentage sign mean in Python

Question

In the tutorial there is an example for finding prime numbers    gt  gt  gt  for n in range 2  10           for x in range 2  n               if n   x    0                  print n   equals   x       n  x                  break         else                loop fell through without finding a factor             print n   is a prime number         I understand that the double    is a test for equality  but I don t understand the if n   x part  Like I can verbally walk through each part and say what the statement does for the example  But I don t understand how the percentage sign falls in    What does if n   x actually say

User · Answer

x   n    0 which means the x n and the value of reminder will taken as a result and compare with zero      example  4 5  0 4 5 reminder is 4 4  0  False

User · Answer

The   does two things  depending on its arguments   In this case  it acts as the modulo operator  meaning when its arguments are numbers  it divides the first by the second and returns the remainder   34   10    4 since 34 divided by 10 is three  with a remainder of four     If the first argument is a string  it formats it using the second argument   This is a bit involved  so I will refer to the documentation  but just as an example     gt  gt  gt   foo  d bar    5  foo 5 bar    However  the string formatting behavior is supplemented as of Python 3 1 in favor of the string format   mechanism      The formatting operations described here exhibit a variety of quirks that lead to a number of common errors  such as failing to display tuples and dictionaries correctly   Using the newer str format   interface helps avoid these errors  and also provides a generally more powerful  flexible and extensible approach to formatting text    And thankfully  almost all of the new features are also available from python 2 6 onwards

User · Answer

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

User · Answer

In python 2 6 the     operator performed a modulus  I don t think they changed it in 3 0 1  The modulo operator tells you the remainder of a division of two numbers

User · Answer

What does the percentage sign mean    It s an operator in Python that can mean several things depending on the context  A lot of what follows was already mentioned  or hinted at  in the other answers but I thought it could be helpful to provide a more extensive summary     for Numbers  Modulo operation   Remainder   Rest  The percentage sign is an operator in Python  It s described as    x   y       remainder of x   y    So it gives you the remainder rest that remains if you  floor divide  x by y  Generally  at least in Python  given a number x and a divisor y   x    y    x    y     x   y    For example if you divide 5 by 2    gt  gt  gt  5    2 2  gt  gt  gt  5   2 1   gt  gt  gt  2    5    2     5   2  5   In general you use the modulo operation to test if a number divides evenly by another number  that s because multiples of a number modulo that number returns 0    gt  gt  gt  15   5    15 is 3   5 0   gt  gt  gt  81   9    81 is 9   9 0   That s how it s used in your example  it cannot be a prime if it s a multiple of another number  except for itself and one   that s what this does   if n   x    0      break   If you feel that n   x    0 isn t very descriptive you could put it in another function with a more descriptive name   def is multiple number  divisor       return number   divisor    0       if is multiple n  x       break   Instead of is multiple it could also be named evenly divides or something similar  That s what is tested here   Similar to that it s often used to determine if a number is  odd  or  even    def is odd number       return number   2    1  def is even number       return number   2    0   And in some cases it s also used for array list indexing when wrap-around  cycling  behavior is wanted  then you just modulo the  index  by the  length of the array  to achieve that    gt  gt  gt  l    0  1  2   gt  gt  gt  length   len l   gt  gt  gt  for index in range 10           print l index   length   0 1 2 0 1 2 0 1 2 0   Note that there is also a function for this operator in the standard library operator mod  and the alias operator   mod       gt  gt  gt  import operator  gt  gt  gt  operator mod 5  2     equivalent to 5   2 1   But there is also the augmented assignment    which assigns the result back to the variable    gt  gt  gt  a   5  gt  gt  gt  a    2    identical to  a   a   2  gt  gt  gt  a 1     for strings  printf-style String Formatting  For strings the meaning is completely different  there it s one way  in my opinion the most limited and ugly  for doing string formatting    gt  gt  gt    s is  s       this    good     this is good    Here the   in the string represents a placeholder followed by a formatting specification  In this case I used  s which means that it expects a string  Then the string is followed by a   which indicates that the string on the left hand side will be formatted by the right hand side  In this case the first  s is replaced by the first argument this and the second  s is replaced by the second argument  good    Note that there are much better  probably opinion-based  ways to format strings    gt  gt  gt      is      format  this    good    this is good       in Jupyter IPython  magic commands  To quote the docs      To Jupyter users  Magics are specific to and provided by the IPython kernel  Whether magics are available on a kernel is a decision that is made by the kernel developer on a per-kernel basis  To work properly  Magics must use a syntax element which is not valid in the underlying language  For example  the IPython kernel uses the   syntax element for magics as   is not a valid unary operator in Python  While  the syntax element has meaning in other languages    This is regularly used in Jupyter notebooks and similar   In  1    a   10          b   20           timeit a   b     one   - gt  line-magic  54 6 ns    2 7 ns per loop  mean    std  dev  of 7 runs  10000000 loops each   In  2      timeit    two    - gt  cell magic           a    b  362 ns    8 4 ns per loop  mean    std  dev  of 7 runs  1000000 loops each    The   operator on arrays  in the NumPy   Pandas ecosystem   The   operator is still the modulo operator when applied to these arrays  but it returns an array containing the remainder of each element in the array    gt  gt  gt  import numpy as np  gt  gt  gt  a   np arange 10   gt  gt  gt  a array  0  1  2  3  4  5  6  7  8  9     gt  gt  gt  a   2 array  0  1  0  1  0  1  0  1  0  1     Customizing the   operator for your own classes  Of course you can customize how your own classes work when the   operator is applied to them  Generally you should only use it to implement modulo operations  But that s a guideline  not a hard rule   Just to provide a simple example that shows how it works   class MyNumber object       def   init   self  value           self value   value      def   mod   self  other           print    mod   called on    r    format self           return self value   other      def   repr   self           return   self   class     name     self value r    format self self    This example isn t really useful  it just prints and then delegates the operator to the stored value  but it shows that   mod   is called when   is applied to an instance    gt  gt  gt  a   MyNumber 10   gt  gt  gt  a   2   mod   called on  MyNumber 10   0   Note that it also works for    without explicitly needing to implement   imod      gt  gt  gt  a   MyNumber 10   gt  gt  gt  a    2   mod   called on  MyNumber 10     gt  gt  gt  a 0   However you could also implement   imod   explicitly to overwrite the augmented assignment   class MyNumber object       def   init   self  value           self value   value      def   mod   self  other           print    mod   called on    r    format self           return self value   other      def   imod   self  other           print    imod   called on    r    format self           self value    other         return self      def   repr   self           return   self   class     name     self value r    format self self    Now    is explicitly overwritten to work in-place    gt  gt  gt  a   MyNumber 10   gt  gt  gt  a    2   imod   called on  MyNumber 10     gt  gt  gt  a MyNumber 0

User · Answer

The modulus operator  The remainder when you divide two number   For Example    gt  gt  gt  5   2   1   remainder of 5 divided by 2 is 1  gt  gt  gt  7   3   1   remainer of 7 divided by 3 is 1  gt  gt  gt  3   1   0   because 1 divides evenly into 3

User · Answer

It checks if the modulo of the division  For example  in the case you are iterating over all numbers from 2 to n and checking if n is divisible by any of the numbers in between  Simply put  you are checking if a given number n is prime   Hint  You could check up to n 2

User · Answer

While this is slightly off-topic  since people will find this by searching for  percentage sign in Python   as I did   I wanted to note that the   sign is also used to prefix a  magic  function in iPython  https   ipython org ipython-doc 3 interactive tutorial html magic-functions

[python] What does the percentage sign mean in Python

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