I have removed the for loop as it is not rubyish in nature, the below should work
require 'octokit'
require 'csv'
client = Octokit::Client.new :login => 'github_username', :password => 'github_password'
repo = 'rubinius/rubinius'
numbers = CSV.read('/Users/Name/Downloads/numbers.csv').flatten
# at this point, essentially numbers = [642, 630, 623, 643, 626]
CSV.open('results.csv', 'w') do |csv|
numbers.each do |number|
begin
pull = client.pull_request(repo, number)
csv << [pull.number, pull.additions, pull.deletions]
rescue
csv << [0,0,0]
next
end
end
end