How to check if string input is a number

Question

How do I check if a user s string input is a number  e g  -1  0  1  etc     user input   input  Enter something     if type user input     int      print  Is a number   else      print  Not a number     The above won t work since input always returns a string

User · Answer

For Python 3 the following will work   userInput   0 while True    try       userInput   int input  Enter something               except ValueError       print  Not an integer         continue   else       print  Yes an integer         break

User · Answer

try this  it worked for me even if I input negative numbers     def length s       return len s      s   input  Enter the String         try          if  type int s     int               print  You input an integer        except ValueError                print  it is a string with length     str length s

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If you wanted to evaluate floats  and you wanted to accept NaNs as input but not other strings like  abc   you could do the following   def isnumber x       import numpy     try          return type numpy float x      float     except ValueError          return False

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Based on inspiration from answer  I defined a function as below  Looks like its working fine  Please let me know if you find any issue  def isanumber inp       try          val   int inp          return True     except ValueError          try              val   float inp              return True         except ValueError              return False

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Simply try converting it to an int and then bailing out if it doesn t work   try     val   int userInput  except ValueError     print  That s not an int

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This works with any number  including a fraction   import fractions  def isnumber s      try       float s       return True    except ValueError       try          Fraction s         return True      except ValueError          return False

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I ve been using a different approach I thought I d share  Start with creating a valid range   valid    str i  for i in range -10 11        -10   -9     10      Now ask for a number and if not in list continue asking   p   input  Enter a number      while p not in valid      p   input  Not valid  Try to enter a number again       Lastly convert to int  which will work because list only contains integers as strings   p   int p

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I know this is pretty late but its to help anyone else that had to spend 6 hours trying to figure this out   thats what I did    This works flawlessly   checks if any letter is in the input checks if input is either integer or float   a  raw input  Amount      try      int a  except ValueError      try          float a      except ValueError          print  This is not a number          a 0   if a  0      a 0 else      print a      Do stuff

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If you specifically need an int or float  you could try  is not int  or  is not float    user input      while user input is not int      try          user input   int input  Enter a number              break     except ValueError          print  Please enter a valid number      print  You entered     format a     If you only need to work with ints  then the most elegant solution I ve seen is the   isdigit    method   a      while a isdigit      False      a   input  Enter a number      print  You entered     format a

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Here is a simple function that checks input for INT and RANGE   Here  returns  True  if input is integer between 1-100   False  otherwise  def validate userInput        try          val   int userInput          if val  gt  0 and val  lt  101              valid   True         else              valid   False      except Exception          valid   False      return valid

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You can use the isdigit   method for strings  In this case  as you said the input is always a string        user input   input  Enter something        if user input isdigit            print  Is a number       else          print  Not a number

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natural   0  1  2     8   Python 2  it is   unicode user input  isnumeric     Python 3  it is   str user input  isnumeric     integer   -8      -2  -1  0  1  2  8   try      int user input      it is   True  except ValueError      it is   False   float   -8      -2  -1 0   1  -1  -0 0   1  0  0 0   1       1  1 0   1        8    try      float user input      it is   True  except ValueError      it is   False

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the most elegant solutions would be the already proposed   a 123 bool a   a isnumeric     Unfortunatelly it doesn t work both for negative integers and for general float values of a  If your point is to check if  a  is a generic number beyond integers i d suggest the following one  which works for every kind of float and integer     Here is the test   def isanumber a        try          float repr a           bool a   True     except          bool a   False      return bool a   a   1   integer isanumber a   gt  gt  gt  True  a   -2 5982347892   general float isanumber a   gt  gt  gt  True  a    1    actually a string isanumber a   gt  gt  gt  False   I hope you find it useful

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Works fine for check if an input is    a positive Integer AND in a specific range  def checkIntValue           Works fine for check if an   input   is    a positive Integer AND in a specific range        maxValue   20     while True          try              intTarget   int input  Your number              except ValueError              continue         else              if intTarget  lt  1 or intTarget  gt  maxValue                  continue             else                  return  intTarget

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Why not divide the input by a number  This way works with everything  Negatives  floats  and negative floats  Also Blank spaces and zero   numList    499  -486  0 1255468  -0 21554   a    this    long string here    455 street area   0       for item in numList       try          print  item   2   You can divide by any number really  except zero     except          print  Not A Number      item   Result   249 -243 0 0627734 -0 10777 Not A Number  a Not A Number  this Not A Number  long string here Not A Number  455 street area 0 Not A Number

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The method isnumeric   will do the job  Documentation for python3 x     gt  gt  gt a    123   gt  gt  gt a isnumeric   True   But remember    gt  gt  gt a    -1   gt  gt  gt a isnumeric   False   isnumeric   returns True if all characters in the string are numeric characters  and there is at least one character   So negative numbers are not accepted

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This solution will accept only integers and nothing but integers   def is number s       while s isdigit      False          s   raw input  Enter only numbers         return int s      Your program starts here     user input   is number raw input  Enter a number

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I also ran into problems this morning with users being able to enter non-integer responses to my specific request for an integer   This was the solution that ended up working well for me to force an answer I wanted   player number   0 while player number    1 and player number   2      player number   raw input  Are you Player 1 or 2         try          player number   int player number      except ValueError          print  Please enter  1  or  2        I would get exceptions before even reaching the try  statement when I used   player number   int raw input  Are you Player 1 or 2        and the user entered  J  or any other non-integer character   It worked out best to take it as raw input  check to see if that raw input could be converted to an integer  and then convert it afterward

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EDITED  You could also use this below code to find out if its a number or also a negative  import re num format   re compile     -   1-9  0-9      0-9      isnumber   re match num format givennumber  if isnumber      print  given string is number    you could also change your format to your specific requirement  I am seeing this post a little too late but hope this helps other persons who are looking for answers       let me know if anythings wrong in the given code

User · Answer

I would recommend this   karthik27  for negative numbers   import re num format   re compile r   -  1-9  0-9      0-9       Then do whatever you want with that regular expression  match    findall   etc

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Here is the simplest solution   a  input  Choose the option n    if int a        print  a   else      print  Try Again

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while True      b1 input  Type a number        try          a1 int b1      except ValueError          print      a1 s  is not a number  Try again      a1  b1              else          print   You typed        format a1           break   This makes a loop to check whether input is an integer or not  result would look like below    gt  gt  gt   Run 1 1 py Type a number d  d  is not a number  Try again  Type a number   gt  gt  gt   Run 1 1 py Type a number 4 You typed 4   gt  gt  gt

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a 10  isinstance a int    True  b  abc   isinstance b int    False

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Apparently this will not work for negative values  but it will for positive numbers     Use isdigit    if userinput isdigit         do stuff

[python] How to check if string input is a number?

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