Take the following scenario which happened to me recently. I am trying to debug an issue on Travis CI involving environment variables. Basically, I am not sure if an environment variable is being set correctly. So in my code, I put

print(os.environ.keys())

The reason I put keys() was 1, I didn't care about the values, and 2, I have secure environment variables set on Travis. 

To my surprise, in the Travis logs, I found something like this

KeysView(environ({'TRAVIS_STACK_FEATURES': 'basic cassandra chromium couchdb disabled-ipv6 docker docker-compose elasticsearch firefox go-toolchain google-chrome jdk memcached mongodb mysql neo4j nodejs_interpreter perl_interpreter perlbrew phantomjs postgresql python_interpreter rabbitmq redis riak ruby_interpreter sqlite xserver', 'CI': 'true', ..., 'MANPATH': '/home/travis/.nvm/versions/node/v7.4.0/share/man:/home/travis/.kiex/elixirs/elixir-1.4.5/man:/home/travis/.rvm/rubies/ruby-2.4.1/share/man:/usr/local/man:/usr/local/clang-3.9.0/share/man:/usr/local/share/man:/usr/share/man:/home/travis/.rvm/man'}))

So instead of just printing the keys like I asked for, it printed the whole environment, plus "KeysView(environ(". Included here was my secure environment variable. 

Now, fortunately, Travis hides the contents of secure environment variables in the logs, but it didn't used to (https://blog.travis-ci.com/2017-05-08-security-advisory).

Aside from being a potential security issue, it's just annoying that it prints the whole environment. The values are much larger than the keys. With a normal dictionary, print(d.keys()) just prints the keys:

>>> print(dict(a=1, b=2).keys())
dict_keys(['a', 'b'])