python variable NameError

Question

I am having trouble with assigning values to vars and then accessing the values  For example     offer users choice for how large of a song list they want to create   in order to determine  roughly  how many songs to copy print   nHow much space should the random song list occupy  n  print  1  100Mb  print  2  250Mb n   tSizeAns   raw input    if tSizeAns    1      tSize    100Mb  elif tSizeAns    2      tSize    250Mb  else      tSize   100Mb      in case user fails to enter either a 1 or 2  print   nYou  want to create a random song list that is     tSize         Traceback returns   Traceback  most recent call last     File    ranSongList py   line 87  in  lt module gt      print   nYou  want to create a random song list that is     tSize       NameError  name  tSize  is not defined   I have read up on python variables and they do not need to be declared so I am thinking they can be created and used on the fly  no  If so I am not quite sure what the traceback is trying to tell me   By the way  it appears as though python does not offer  case  capabilities  so if anyone has any suggestions how to better offer users lists from which to choose options and assign var values I would appreciate reading them  Eventually when time allows I will learn Tkinter and port to GUI

User · Accepted Answer

Your if statements are checking for int values   raw input returns a string   Change the following line   tSizeAns   raw input     to  tSizeAns   int raw input

User · Answer

Initialize tSize to   tSize         before your if block to be safe  Also in your else case  put tSize in quotes so it is a string not an int  Also also you are comparing strings to ints

User · Answer

I would approach it like this   sizes    100  250  print  How much space should the random song list occupy   print   n  join   0    1 Mb  format n  s                  for n  s in enumerate sizes  1     present choices choice   int raw input  Enter choice       throws error if not int size   sizes 0    safe starting choice if choice in range 2  len sizes    1       size   sizes choice - 1    note index offset from choice print  You  want to create a random song list that is  0 Mb   format size    You could also loop until you get an acceptable answer and cover yourself in case of error   choice   0 while choice not in range 1  len sizes    1     loop     try    guard against error         choice   int raw input           except ValueError    couldn t make an int         print  Please enter a number          choice   0 size   sizes choice - 1    now definitely valid

User · Answer

This should do it      usr local cpython-2 7 bin python    offer users choice for how large of a song list they want to create   in order to determine  roughly  how many songs to copy print   nHow much space should the random song list occupy  n  print  1  100Mb  print  2  250Mb n   tSizeAns   int raw input     if tSizeAns    1      tSize    100Mb  elif tSizeAns    2      tSize    250Mb  else      tSize    100Mb       in case user fails to enter either a 1 or 2  print   nYou  want to create a random song list that is      format tSize    BTW  in case you re open to moving to Python 3 x  the differences are slight      usr local cpython-3 3 bin python    offer users choice for how large of a song list they want to create   in order to determine  roughly  how many songs to copy print   nHow much space should the random song list occupy  n   print  1  100Mb   print  2  250Mb n    tSizeAns   int input     if tSizeAns    1      tSize    100Mb  elif tSizeAns    2      tSize    250Mb  else      tSize    100Mb       in case user fails to enter either a 1 or 2  print   nYou want to create a random song list that is      format tSize     HTH

User · Answer

In addition to the missing quotes around 100Mb in the last else  you also want to quote the constants in your if-statements if tSizeAns     1    because raw input returns a string  which in comparison with an integer will always return false   However the missing quotes are not the reason for the particular error message  because it would result in an syntax error before execution  Please check your posted code  I cannot reproduce the error message   Also if     elif     else in the way you use it is basically equivalent to a case or switch in other languages and is neither less readable nor much longer  It is fine to use here  One other way that might be a good idea to use if you just want to assign a value based on another value is a dictionary lookup   tSize     1    100Mb    2    200Mb   tSizeAns    This however does only work as long as tSizeAns is guaranteed to be in the range of tSize  Otherwise you would have to either catch the KeyError exception or use a defaultdict   lookup     1    100Mb    2    200Mb   try      tSize   lookup tSizeAns  except KeyError      tSize    100Mb    or  from collections import defaultdict         lookup   defaultdict lambda   100Mb     1    100Mb    2    200Mb    tSize   lookup tSizeAns    In your case I think these methods are not justified for two values  However you could use the dictionary to construct the initial output at the same time

[python] python variable NameError

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