How to test multiple variables against a value

Question

I m trying to make a function that will compare multiple variables to an integer and output a string of three letters  I was wondering if there was a way to translate this into Python  So say   x   0 y   1 z   3 mylist       if x or y or z    0       mylist append  c   if x or y or z    1       mylist append  d   if x or y or z    2       mylist append  e   if x or y or z    3        mylist append  f     which would return a list of     c    d    f     Is something like this possible

User · Accepted Answer

You misunderstand how boolean expressions work; they don't work like an English sentence and guess that you are talking about the same comparison for all names here. You are looking for:

if x == 1 or y == 1 or z == 1:

x and y are otherwise evaluated on their own (False if 0, True otherwise).

You can shorten that using a containment test against a tuple:

if 1 in (x, y, z):

or better still:

if 1 in {x, y, z}:

using a set to take advantage of the constant-cost membership test (in takes a fixed amount of time whatever the left-hand operand is).

When you use or, python sees each side of the operator as separate expressions. The expression x or y == 1 is treated as first a boolean test for x, then if that is False, the expression y == 1 is tested.

This is due to operator precedence. The or operator has a lower precedence than the == test, so the latter is evaluated first.

However, even if this were not the case, and the expression x or y or z == 1 was actually interpreted as (x or y or z) == 1 instead, this would still not do what you expect it to do.

x or y or z would evaluate to the first argument that is 'truthy', e.g. not False, numeric 0 or empty (see boolean expressions for details on what Python considers false in a boolean context).

So for the values x = 2; y = 1; z = 0, x or y or z would resolve to 2, because that is the first true-like value in the arguments. Then 2 == 1 would be False, even though y == 1 would be True.

The same would apply to the inverse; testing multiple values against a single variable; x == 1 or 2 or 3 would fail for the same reasons. Use x == 1 or x == 2 or x == 3 or x in {1, 2, 3}.

User · Answer

I think this will handle it better   my dict    0   c   1   d   2   e   3   f    def validate x  y  z       for ele in  x  y  z           if ele in my dict keys                return my dict ele    Output   print validate 0  8  9  c print validate 9  8  9  None print validate 9  8  2  e

User · Answer

As stated by Martijn Pieters  the correct  and fastest  format is   if 1 in  x  y  z     Using his advice you would now have separate if-statements so that Python will read each statement whether the former were True or False  Such as   if 0 in  x  y  z       mylist append  c   if 1 in  x  y  z       mylist append  d   if 2 in  x  y  z       mylist append  e         This will work  but if you are comfortable using dictionaries  see what I did there   you can clean this up by making an initial dictionary mapping the numbers to the letters you want  then just using a for-loop   num to letters    0   c   1   d   2   e   3   f   for number in num to letters      if number in  x  y  z           mylist append num to letters number

User · Answer

Problem  While the pattern for testing multiple values   gt  gt  gt  2 in  1  2  3  True  gt  gt  gt  5 in  1  2  3  False   is very readable and is working in many situation  there is one pitfall    gt  gt  gt  0 in  True  False  True   But we want to have   gt  gt  gt   0 is True  or  0 is False  False   Solution  One generalization of the previous expression is based on the answer from ytpillai    gt  gt  gt  any  0 is True  0 is False   False   which can be written as   gt  gt  gt  any 0 is item for item in  True  False   False   While this expression returns the right result it is not as readable as the first expression  -

User · Answer

It can be done easily as   for value in  var1 var2 var3        li append  targetValue

User · Answer

All of the excellent answers provided here concentrate on the specific requirement of the original poster and concentrate on the if 1 in  x y z  solution put forward by Martijn Pieters  What they ignore is the broader implication of the question  How do I test one variable against multiple values  The solution provided will not work for partial hits if using strings for example  Test if the string  Wild  is in multiple values   gt  gt  gt  x    Wild things   gt  gt  gt  y    throttle it back   gt  gt  gt  z    in the beginning   gt  gt  gt  if  Wild  in  x  y  z   print  True         or   gt  gt  gt  x    Wild things   gt  gt  gt  y    throttle it back   gt  gt  gt  z    in the beginning   gt  gt  gt  if  Wild  in  x  y  z   print  True         for this scenario it s easiest to convert to a string   gt  gt  gt   x  y  z    Wild things    throttle it back    in the beginning    gt  gt  gt   x  y  z    in the beginning    throttle it back    Wild things    gt  gt  gt     gt  gt  gt  if  Wild  in str  x  y  z    print  True       True  gt  gt  gt  if  Wild  in str  x  y  z    print  True       True   It should be noted however  as mentioned by  codeforester  that word boundries are lost with this method  as in        gt  gt  gt  x   Wild things    throttle it back    in the beginning    gt  gt  gt  if  rot  in str x   print True       True   the 3 letters rot do exist in combination in the list but not as an individual word  Testing for   rot   would fail but if one of the list items were  rot in hell   that would fail as well  The upshot being  be careful with your search criteria if using this method and be aware that it does have this limitation

User · Answer

Without dict  try this solution   x  y  z   0  1  3     offset   ord  c    chr i   offset  for i in  x y z     and gives     c    d    f

User · Answer

Looks like you re building some kind of Caesar cipher   A much more generalized approach is this   input values    0  1  3  origo   ord  c    chr val   origo  for val in inputs    outputs    c    d    f     Not sure if it s a desired side effect of your code  but the order of your output will always be sorted   If this is what you want  the final line can be changed to   sorted  chr val   origo  for val in inputs

User · Answer

You can try the method shown below  In this method  you will have the freedom to specify input the number of variables that you wish to enter   mydict    0  c   1  d   2  e   3  f   mylist      num var   int raw input  How many variables       Enter 3 when asked for input   for i in range num var            Enter 0 as first input  1 as second input and 3 as third input         globals    var  str  i   zfill 3     int raw input  Enter an integer between 0 and 3         mylist    mydict globals    var  str  i   zfill 3     print mylist  gt  gt  gt    c    d    f

User · Answer

One line solution   mylist     0   c   1   d   2   e   3   f   i  for i in  0  1  2  3  if i in  x  y  z     Or   mylist     cdef  i  for i in range 4  if i in  x  y  z

User · Answer

If you want something very interesting solution  refer below  x   0 y   1 z   3 mylist       if any i in  0  for i in x y z        mylist append  quot c quot   if any i in  1  for i in x y z        mylist append  quot d quot   if any i in  2  for i in x y z        mylist append  quot e quot   if any i in  3  for i in x y z        mylist append  quot f quot    It is a mix of list comprehension and any keyword

User · Answer

Set is the good approach here  because it orders the variables  what seems to be your goal here   z y x  is  0 1 3  whatever the order of the parameters    gt  gt  gt    cdef  i  for i in  z x y     c    d    f     This way  the whole solution is O n

User · Answer

The direct way to write x or y or z    0 is  if any map  lambda value  value    0    x y z         pass   write your logic    But I dont think  you like it     And this way is ugly   The other way  a better  is   0 in  x  y  z    BTW lots of ifs could be written as something like this  my cases         0  Mylist append  c        1  Mylist append  d               for key in my cases      if key in  x y z           my cases key            break

User · Answer

Maybe you need direct formula for output bits set   x 0 or y 0 or z 0   is equivalent to x y z   0  x 1 or y 1 or z 1   is equivalent to  x-1   y-1   z-1  0  x 2 or y 2 or z 2   is equivalent to  x-2   y-2   z-2  0   Let s map to bits   c  1  d  0xb10  e  0xb100  f  0xb1000  Relation of isc  is  c     if xyz 0 then isc 1 else isc 0   Use math if formula https   youtu be KAdKCgBGK0k list PLnI9xbPdZUAmUL8htSl6vToPQRRN3hhFp amp t 315   c    xyz 0 and isc 1  or    xyz 0 and isc 1  or  isc 0   and  isc 0     d     x-1  y-1  z-1  0 and isc 2  or    xyz 0 and isd 2  or  isc 0   and  isc 0         Connect these formulas by following logic    logic and is the sum of squares of equations logic or is the product of equations   and you ll have a total equation express sum and you have total formula of sum  then sum amp 1 is c  sum amp 2 is d  sum amp 4 is e  sum amp 5 is f  After this you may form predefined array where index of string elements would correspond to ready string   array sum  gives you the string

User · Answer

The most pythonic way of representing your pseudo-code in Python would be  x   0 y   1 z   3 mylist       if any v    0 for v in  x  y  z        mylist append  quot c quot   if any v    1 for v in  x  y  z        mylist append  quot d quot   if any v    2 for v in  x  y  z        mylist append  quot e quot   if any v    3 for v in  x  y  z        mylist append  quot f quot

User · Answer

To check if a value is contained within a set of variables you can use the inbuilt modules           itertools and operator   For example   Imports   from itertools import repeat from operator import contains   Declare variables   x   0 y   1 z   3   Create mapping of values  in the order you want to check    check values    0  1  3    Use itertools to allow repetition of the variables   check vars   repeat  x  y  z     Finally  use the map function to create an iterator   checker   map contains  check vars  check values    Then  when checking for the values  in the original order   use next     if next checker     Checks for 0       Do something     pass elif next checker     Checks for 1       Do something     pass   etc     This has an advantage over the lambda x  x in  variables  because operator is an inbuilt module and is faster and more efficient than using lambda which has to create a custom in-place function   Another option for checking if there is a non-zero  or False  value in a list   not  x and y and z    Equivalent   not all  x  y  z

User · Answer

If you want to use if  else statements following is another solution   myList      aList    0  1  3   for l in aList      if l  0  myList append  c       elif l  1  myList append  d       elif l  2  myList append  e       elif l  3  myList append  f    print myList

User · Answer

This will help you   def test fun val       x   0     y   1     z   2     myList          if val in  x  y  z  and val    0          myList append  C       if val in  x  y  z  and val    1          myList append  D       if val in  x  y  z  and val    2          myList append  E    test fun 2

User · Answer

You can unite this  x   0 y   1 z   3   in one variable   In  1   xyz    0 1 3    In  2   mylist        Change our conditions as   In  3   if 0 in xyz                mylist append  c             if 1 in xyz                mylist append  d             if 2 in xyz                mylist append  e             if 3 in xyz                 mylist append  f      Output   In  21   mylist                                                                                 Out 21     c    d    f

User · Answer

If you ARE very very lazy  you can put the values inside an array  Such as  list      list append x  list append y  list append z  nums    add numbers here  letters    add corresponding letters here  for index in range len nums        for obj in list          if obj    num index               MyList append letters index               break   You can also put the numbers and letters in a dictionary and do it  but this is probably a LOT more complicated than simply if statements  That s what you get for trying to be extra lazy     One more thing  your   if x or y or z    0    will compile  but not in the way you want it to  When you simply put a variable in an if statement  example   if b   the program will check if the variable is not null  Another way to write the above statement  which makes more sense  is   if bool b    Bool is an inbuilt function in python which basically does the command of verifying a boolean statement  If you don t know what that is  it is what you are trying to make in your if statement right now      Another lazy way I found is    if any  x  0  y  0  z  0

User · Answer

To test multiple variables with one single value  if 1 in  a b c    To test multiple values with one variable  if a in  1  2  3

User · Answer

This code may be helpful  L   x  y  z  T    0  c    1  d    2  e    3  f     List2    for t in T   if t 0  in L       List2 append t 1       break

User · Answer

d    0  c   1  d   2  e   3   f   x  y  z    0  1  3  print  v for  k v  in d items   if x  k or y  k or z  k

User · Answer

Your problem is more easily addressed with a dictionary structure like   x   0 y   1 z   3 d    0   c   1  d   2  e   3  f   mylist    d k  for k in  x  y  z

User · Answer

You can use dictionary    x   0 y   1 z   3 list    dict    0   c   1   d   2   e   3   f   if x in dict      list append dict x   else      pass  if y in dict      list append dict y   else      pass if z in dict      list append dict z   else      pass  print list

User · Answer

you can develop it through two ways     def compareVariables x y z           mylist              if x  0 or y  0 or z  0              mylist append  c           if  x  1 or y  1 or z  1              mylist append  d           if  x  2 or y  2 or z  2              mylist append  e           if  x  3 or y  3 or z  3              mylist append  f           else              print  quot wrong input value  quot           print  first   mylist           compareVariables 1  3  2   Or     def compareVariables x y z           mylist              if 0 in  x y z                mylist append  c           if 1 in  x y z                mylist append  d           if 2 in  x y z                mylist append  e           if 3 in  x y z                mylist append  f           else               print  quot wrong input value  quot           print  second   mylist           compareVariables 1  3  2

[python] How to test multiple variables against a value?

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