The tilde operator in Python

Question

What s the usage of the tilde operator in Python   One thing I can think about is do something in both sides of a string or list  such as check if a string is palindromic or not   def is palindromic s       return all s i     s  i  for i in range len s    2      Any other good usage

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is the bitwise complement operator in python which essentially calculates -x - 1  So a table would look like  i   i   0  -1 1  -2 2  -3 3  -4  4  -5  5  -6   So for i   0 it would compare s 0  with s len s  - 1   for i   1  s 1  with s len s  - 2    As for your other question  this can be useful for a range of bitwise hacks

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One should note that in the case of array indexing  array  i  amounts to reversed array i   It can be seen as indexing starting from the end of the array    0  1  2  3  4  5  6  7  8                              i                 i

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Besides being a bitwise complement operator    can also help revert a boolean value  though it is not the conventional bool type here  rather you should use numpy bool      This is explained in   import numpy as np assert  np True     np False      Reversing logical value can be useful sometimes  e g   below   operator is used to cleanse your dataset and return you a column without NaN   from numpy import NaN import pandas as pd  matrix   pd DataFrame  1 2 3 4 NaN   columns   Number    dtype  float64     Remove NaN in column  Number  matrix  Number    matrix  Number   isnull

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It is a unary operator  taking a single argument  that is borrowed from C  where all data types are just different ways of interpreting bytes   It is the  invert  or  complement  operation  in which all the bits of the input data are reversed   In Python  for integers  the bits of the twos-complement representation of the integer are reversed  as in b  lt - b XOR 1 for each individual bit   and the result interpreted again as a twos-complement integer   So for integers   x is equivalent to  -x  - 1   The reified form of the   operator is provided as operator invert   To support this operator in your own class  give it an   invert   self  method    gt  gt  gt  import operator  gt  gt  gt  class Foo        def   invert   self           print  invert       gt  gt  gt  x   Foo    gt  gt  gt  operator invert x  invert  gt  gt  gt   x invert   Any class in which it is meaningful to have a  complement  or  inverse  of an instance that is also an instance of the same class is a possible candidate for the invert operator   However  operator overloading can lead to confusion if misused  so be sure that it really makes sense to do so before supplying an   invert   method to your class    Note that byte-strings  ex    xff   do not support this operator  even though it is meaningful to invert all the bits of a byte-string

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I was solving this leetcode problem and I came across this beautiful solution by a user named Zitao Wang   The problem goes like this for each element in the given array find the product of all the remaining numbers without making use of divison and in O n  time  The standard solution is   Pass 1  For all elements compute product of all the elements to the left of it Pass 2  For all elements compute product of all the elements to the right of it         and then multiplying them for the final answer    His solution uses only one for loop by making use of  He computes the left product and right product on the fly using    def productExceptSelf self  nums       res    1  len nums      lprod   1     rprod   1     for i in range len nums            res i     lprod         lprod    nums i          res  i     rprod         rprod    nums  i      return res

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The only time I ve ever used this in practice is with numpy pandas   For example  with the  isin   dataframe method   In the docs they show this basic example   gt  gt  gt  df isin  0  2           num legs  num wings falcon      True       True dog        False       True   But what if instead you wanted all the rows not in  0  2       gt  gt  gt   df isin  0  2           num legs  num wings falcon     False       False dog        True        False

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This is minor usage is tilde     def split train test by id data  test ratio  id column       ids   data id column      in test set   ids apply lambda id   test set check id   test ratio        return data loc  in test set   data loc in test set    the code above is from  Hands On Machine Learning   you use tilde    sign  as alternative to - sign index marker  just like you use minus - is for integer index  ex    array    1 2 3 4 5 6  print array -1     is the samething as  print array  1

[python] The tilde operator in Python

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