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Efficient debugging with Pry
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Conrad Irwin
October 02, 2012
Programming
2
360
Efficient debugging with Pry
A short talk summarizing how to use Pry to save yourself time when debugging.
Conrad Irwin
October 02, 2012
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Transcript
None
Debugging l Figure out why the code is broken l
Fix it l Repeat.
puts l Most common debugging tool l Very easy to
use l Gather information one chunk at a time
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
pry-rescue l Automatic binding.pry on unhandled exceptions l `gem install
pry-rescue` l Reduces feedback cycle times
NoMethodError l Most common exception in ruby code? l Caused
by: - Typos - Forgetting the right method name - Using the wrong object
ls -‐-‐grep l Finds the correct method l No
need to google l Doesn't rely on gems having docs ;)
[1] pry(main)> ls Base64 -‐-‐grep encode Base64.methods:
encode64 strict_encode64 urlsafe_encode64 [2] pry(main)>
ls -‐-‐grep l Finds the correct method l No
need to google l Doesn't rely on gems having docs ;)
edit -‐-‐ex l Opens your text editor l Jumps
to the exception l Reloads the code when you're done
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)>
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
None
[1] pry(main)> edit -‐-‐ex 3: def
base64ify(email) => 4: Base64.encode64(email) 5: end [2] pry(main)> base64ify("hello world") "aGVsbG8gd29ybGQ=\n"
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`
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)>
[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"}
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`
$ and ? l show-source and show-doc l Instant documentation
when you need it l No need to `cd` into gem directories.
[1] pry(main)> $ safe_title 2: def
safe_title(post) 3: make_safe(post[:title]) 4: end [2] pry(main)>
[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)>
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
<EOF> l @ConradIrwin (github, twitter, gmail, etc.) l http://pryrepl.org/ l
irc://freenode.net/#pry