#with statement

[linuxfollies]

Python's with statement

Old habits die hard. I learned a long time ago (Python 1.x) this pattern for opening and operating on files:

try:    

f = open("filename.txt", "ro")

try:

        for l in f:

            print l

    finally:

        f.close()

except IOError as e:

print "I/O error({0}): {1}".format(e.errno, e.strerror)

Since Python 2.6, the with statement does this automatically:

with open("filename.txt", "ro") as f:

    for l in f:

        print l

The with statement works with some other classes, too. PS Blogger really needs a code block style. via Blogger http://bit.ly/1toulJ9

[obscurejavascript]

Emulating the With Statement in JavaScript

The JavaScript with statement can be a useful shortcut for accessing object properties:

var mailBox = { messages: { message1: 'hello', message2: 'I could not think of a message' } }; with(mailBox.messages){ console.log(message1); console.log(message2); }

Unfortunately, it is not very cross browser and will be phased out of JavaScript. So it is better to make a custom one:

var with_ = function(obj, callback) { var args = [] for (var property in obj){ args.push(obj[property]); } // Apply sets the context for the function and passes it args // specified by the array. callback.apply(null, args); }; with_(mailBox.messages, function(message1, message2){ console.log(message1); console.log(message2); });

But this still involves specifying function parameters, By defining a wrapper function it is possible to get rid of this:

var with_ = function(obj, callback) { var names = [], values = []; for (var property in obj){ names.push(property); values.push(obj[property]); } // Create wrapper that runs the original function with the obj properties // as parameters var wrapper = Function.apply(null, names.concat('(' + callback + ')();')); // Execute the wrapper with the values of the object wrapper.apply(null, values); }; with_(mailBox.messages, function(){ console.log(message1); console.log(message2); });

Github Location: https://github.com/Jacob-Friesen/obscurejs/blob/master/2014/withEmulation.js