Efficient debugging with Pry

A short talk summarizing how to use Pry to save yourself time when debugging.

Transcript

1. View Slide

2. Debugging
   l 
   Figure out why the code is broken
   l 
   Fix it
   l 
   Repeat.
   

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3. puts
   l 
   Most common debugging tool
   l 
   Very easy to use
   l 
   Gather information one chunk at a time
   

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4. binding.pry
   l 
   Opens pry at that line in your code
   l 
   `gem install pry`
   l 
   Gather as much information as you need
   l 
   Test theories immediately
   

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5. pry-rescue
   l 
   Automatic binding.pry on unhandled exceptions
   l 
   `gem install pry-rescue`
   l 
   Reduces feedback cycle times
   

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6. NoMethodError
   l 
   Most common exception in ruby code?
   l 
   Caused by:
   -  Typos
   -  Forgetting the right method name
   -  Using the wrong object
   

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7. ls  -­‐-­‐grep
    
   l 
   Finds the correct method
   l 
   No need to google
   l 
   Doesn't rely on gems having docs ;)
   

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8.  
    
   [1]  pry(main)>  ls  Base64  -­‐-­‐grep  encode  
   Base64.methods:  encode64    
   strict_encode64    urlsafe_encode64  
   [2]  pry(main)>  
   

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9. ls  -­‐-­‐grep
    
   l 
   Finds the correct method
   l 
   No need to google
   l 
   Doesn't rely on gems having docs ;)
   

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10. edit  -­‐-­‐ex
     
    l 
    Opens your text editor
    l 
    Jumps to the exception
    l 
    Reloads the code when you're done
    

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11. From:  /0/ruby/pry/example.rb  @  line  3:  
           3:  def  base64ify(email)  
     =>  4:      Base64.encode(email)  
           5:  end  
    NoMethodError:  undefined  method  
    `encode'  for  Base64:Module'  
    [1]  pry(main)>    
    

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12. From:  /0/ruby/pry/example.rb  @  line  3:  
           3:  def  base64ify(email)  
     =>  4:      Base64.encode(email)  
           5:  end  
    NoMethodError:  undefined  method  
    `encode'  for  Base64:Module'  
    [1]  pry(main)>  edit  -­‐-­‐ex  
    

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13. View Slide

14. [1]  pry(main)>  edit  -­‐-­‐ex  
           3:  def  base64ify(email)  
     =>  4:      Base64.encode64(email)  
           5:  end  
     
    [2]  pry(main)>  base64ify("hello  world")  
    "aGVsbG8gd29ybGQ=\n"  
    

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15. up and down
    l 
    Moves pry up and down the call stack
    l 
    Figure out why you have the wrong object
    l 
    Discover why a gem doesn't work
    l 
    `gem install pry-stack_explorer`
    

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16. From:  /0/ruby/pry/example2.rb  @  line  2:  
           2:  def  make_safe(text)  
     =>  3:      text.gsub(/[^a-­‐z]/i,  '-­‐')  
           4:  end  
    NoMethodError:  undefined  method  `gsub'  
    for  nil:NilClass'  
    [1]  pry(main)>    
    

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17. [1]  pry(main)>  up  
    From:  /0/ruby/pry/example2.rb  @  line  6:  
           2:  def  safe_title(post)  
     =>  3:      make_safe(post[:title])  
           4:  end  
    [2]  pry(main)>  post  
    {"title"  =>  "Hello  Pry"}  
    

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18. up and down
    l 
    Moves pry up and down the call stack
    l 
    Figure out why you have the wrong object
    l 
    Discover why a gem doesn't work
    l 
    `gem install pry-stack_explorer`
    

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19. $ and ?
    l 
    show-source and show-doc
    l 
    Instant documentation when you need it
    l 
    No need to `cd` into gem directories.
    

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20. [1]  pry(main)>  $  safe_title  
           2:  def  safe_title(post)  
           3:      make_safe(post[:title])  
           4:  end  
    [2]  pry(main)>  
    

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21. [2]  pry(main)>  ?  safe_title  
    Convert  the  title  of  the  blog  into  a  
    string  suitable  for  use  in  URLs.  
     
    param  [Hash]  post  
    return  [String]  
    [3]  pry(main)>  
    

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22. In conclusion
    l 
    Debugging requires gathering information
    l 
    Get into a `binding.pry` habit
    l 
    Explore pry's extra features
    -  gem install pry-full
    -  Type `help` inside pry
    

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23. 
    l 
    @ConradIrwin (github, twitter, gmail, etc.)
    l 
    http://pryrepl.org/
    l 
    irc://freenode.net/#pry
    

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