ValueError max arg is an empty sequence

Question

I ve created a GUI using wxFormBuilder that should allow a user to enter the names of  visitors to a business  into a list and then click one of two buttons to return the most frequent and least frequent visitors to the business    I created an earlier version that  unfortunately  gave me the range of visitors  rather than the name of the most least frequent visitor  I ve attached a screenshot of the GUI I ve created to help add a little clarity to the issue   http   imgur com XJnvo0U      A new code version takes a different tack than the earlier version  and I can t get it to throw anything  Instead  I keep receiving this error     ValueError  max   arg is an empty sequence  In relation to this line    self txtResults Value   k index max v    import wx import myLoopGUI import commands  class MyLoopFrame myLoopGUI MyFrame1       def   init   self  parent           myLoopGUI MyFrame1   init   self  parent       def clkAddData self parent           if len self txtAddData Value     0              try                  myname   str self txtAddData Value                  self listMyData Append str myname               except                  wx MessageBox  This has to be a name                        else              wx MessageBox  This can t be empty           def clkFindMost self  parent           self listMyData              unique names   set self listMyData          frequencies              for name in unique names              if frequencies get name                   frequencies name     1             else                  frequencies name    0          v   list frequencies values            k   list frequencies keys            self txtResults Value   k index max v         def clkFindLeast self  parent           unique names   set self listMyData          frequencies              for name in unique names              if frequencies get name                   frequencies name     1             else                  frequencies name    0          v   list frequencies values            k   list frequencies keys            self txtResults Value   k index min v    myApp   wx App False  myFrame   MyLoopFrame None  myFrame Show   myApp MainLoop

User · Answer

in one line   v   max v  if v else None   gt  gt  gt  v       gt  gt  gt  max v  Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  ValueError  max   arg is an empty sequence  gt  gt  gt  v   max v  if v else None  gt  gt  gt  v  gt  gt  gt

User · Answer

When the length of v will be zero  it ll give you the value error    You should check the length or you should check the list first whether it is none or not   if list      k index max list     or   len list    0

User · Answer

I realized that I was iterating over a list of lists where some of them were empty  I fixed this by adding this preprocessing step  tfidfLsNew    x for x in tfidfLs if x         the len   of the original was 3105  and the len   of the latter was 3101  implying that four of my lists were completely empty  After this preprocess my max   min   etc  were functioning again

User · Answer

Since you are always initialising self listMyData to an empty list in clkFindMost your code will always lead to this error  because after that both unique names and frequencies are empty iterables  so fix this   Another thing is that since you re iterating over a set in that method then calculating frequency makes no sense as set contain only unique items  so frequency of each item is always going to be 1   Lastly dict get is a method not a list or dictionary so you can t use    with it   Correct way is   if frequencies get name     And Pythonic way is   if name in frequencies    The Pythonic way to get the frequency of items is to use collections Counter   from collections import Counter    Add this at the top of file   def clkFindMost self  parent             self listMyData                 if self listMyData             frequencies   Counter self listMyData             self txtResults Value   max frequencies  key frequencies get          else             self txtResults Value           max   and min   throw such error when an empty iterable is passed to them  You can check the length of v before calling max   on it    gt  gt  gt  lst       gt  gt  gt  max lst   Traceback  most recent call last     File   lt pyshell 2 gt    line 1  in  lt module gt      max lst  ValueError  max   arg is an empty sequence  gt  gt  gt  if lst      mx   max lst  else       Handle this here   If you are using it with an iterator then you need to consume the iterator first before calling max   on it because boolean value of iterator is always True  so we can t use if on them directly    gt  gt  gt  it   iter      gt  gt  gt  bool it  True  gt  gt  gt  lst   list it   gt  gt  gt  if lst         mx   max lst      else         Handle this here      Good news is starting from Python 3 4 you will be able to specify an optional return value for min   and max   in case of empty iterable

User · Answer

try parsing a default value which can be returned by max if length of v none  max v  default 0

[python] ValueError: max() arg is an empty sequence

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