Python ValueError: too many values to unpack with string formatting

Question

I am creating the html for an email using a Python string, like so:

      # Code setting up the message html
      message = "long html message string"

      scoped = ""
      if settings.DEBUG:
          scoped = "scoped"

      header = """                                                                
          <style %s type='text/css'>                                              
              @media only screen and (max-width: 480px){                          
                  .emailImage{                                                    
                      height:auto !important;                                     
                      max-width:200px !important;                                 
                      width: 100% !important;                                     
                  }                                                               
              }                                                                   
          </style>                                                                
          """ % scoped
      footer = "html message footer"

      message = header + message + footer

      # Code sending the message.

The problem is, the above code gives me the error ValueError: too many values to unpack. However, if I remove the scoped variable from the message, the html runs, i.e., this works (albeit without adding the scoped variable into my HTML as I want it to).

      # Code setting up the message html
      message = "long html message string"

      header = """                                                                
          <style type='text/css'>                                              
              @media only screen and (max-width: 480px){                          
                  .emailImage{                                                    
                      height:auto !important;                                     
                      max-width:200px !important;                                 
                      width: 100% !important;                                     
                  }                                                               
              }                                                                   
          </style>                                                                
          """
      footer = "html message footer"

      message = header + message + footer

      # Code sending the message.

Why is the first version throwing that error, and how can I address the ValueError?

Why are you building up HTML by string substitution? That is what templates are for. — Daniel Roseman
– Daniel Roseman, Commented Jun 12, 2015 at 6:55

Eric Appelt · Accepted Answer · 2015-06-11 21:04:24Z

4

You have an unescaped % symbol after the width element, add another % to escape it:

  header = """                                                                
      <style %s type='text/css'>                                              
          @media only screen and (max-width: 480px){                          
              .emailImage{                                                    
                  height:auto !important;                                     
                  max-width:200px !important;                                 
                  width: 100%% !important;                                     
              }                                                               
          }                                                                   
      </style>                                                                
      """ % scoped

Note that when you got rid of the % scoped, you were no longer formatting the string and the % character was no longer special.

answered Jun 11, 2015 at 21:04

Eric Appelt

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2 Comments

YPCrumble Over a year ago

Yes! I had earlier tried to escape it with \% and that didn't work - you have to escape using another % in this context?

Eric Appelt Over a year ago

Yea, in the old style formatting it is very similar to C printf where you also escape % with another %

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