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All of the Python You Need to Forget to Use Repy

This tutorial is written for those who are familiar with the Python programming language, and want to start using Repy. The syntax and many of the properties of Repy should be very familiar for Python users, but there are some noticeable differences.

Many Python built-ins are not allowed in Repy. This is to ensure maximum cross platform compatibility and security for end users. Python modules aren't allowed to be imported (see below), however porting python code to Repy takes minimal effort.

Global Variables

In Repy global variables are not allowed. In place of this there is an implicit dictionary called mycontext which can be used to create globally visible variables.

mycontext['pagecount'] = mycontext['pagecount'] + 1

Import statements

In Repy there are no import statements. In its place make use of the include statement. include takes the specified file and inlines its content to that place in the Repy program.

If you have the file ''a.repy'':

def foo():
  print "foo"

And a file ''b.repy'':

include a.repy
def bar():
  print "bar"

You can use the repy preprocessor to produce a file like:

def foo():
  print "foo"

def bar():
  print "bar"

To do this run python repypp.py b.repy out.repy. The a.repy file does not need to be pre-processed also. The file out.repy will contain the code for a.repy included inside the code for b.repy at the appropriate place.

Input

There are no Repy mechanisms to read user input. Providing the python input and raw_input methods is impractical, since the intent of Repy is to run as a background process on user machines. There is no terminal to accept input from.

Python Built-Ins Not in Repy

Below is a list of the Python built-ins that are not allowed in Repy

  • all
  • any
  • bin
  • callable
  • compile
  • complex
  • delattr
  • dir
  • enumerate
  • eval
  • execfile
  • globals
  • hash
  • help
  • id
  • input
  • iter
  • lambda
  • locals
  • next
  • property
  • raw_input
  • reload
  • reversed
  • sorted
  • staticmethod
  • super
  • unichr
  • unicode
  • vars
  • yield
  • !import!

Common Python Constructs and Their Repy Counterparts

sys.argv

Programs written in Python use sys.argv to access arguments to the file. In Repy the variable callargs behaves the same as sys.argv[1:]

__name__

There is no __name__ variable. In python it's common to use the following code to see if a file invoked directly:

if __name__ == "__main__":
 main()

In Repy the corresponding implicit variable is callfunc. A similar Repy program would include: python if callfunc == "initialize": main()

This ensures that the following code is only executed once. Note that if you use the Repy include statement and the above if statement, both files' initialize blocks will be executed.

Repy scripts are called twice: on entry callfunc is set to "intialize". At exit callfunc is surprisingly enough called "exit".

Python Modules

Python modules aren't directly allowed in Repy. This is to ensure safety for Seattle users, so all code run in a VM can be strictly controlled. Many Python modules have Repy equivalents, which are listed below:

Files

open()

Repy has a builtin open() that behaves similarly to the Python native open.

The file to be opened may only contain the characters 'a-zA-Z0-9.-_', and cannot be . or ..

The object returned by open() is similar to the Python [file] object, and provides most of the same functionality.

os.listdir()

Repy provides the function listdir() which is equivalent to a call to Python python os.listdir('.') Since file access is only allowed within a VM, there is no need to provide listdir() with any arguments. The list will contain all the files in the current working directory.

os.remove()

Remove a file from the user program area. Has the same filename character restrictions as open The following Repy code python removefile(f) Is equivalent to the following Python python os.remove(f)

Time

time.sleep()

Repy's sleep() function behaves similarly to [time.sleep()], causing execution of the current program to halt for the specified number of seconds.

Timer

In python, to start a timer you typically have code such as: ```python def hello(str): print "hello,", str

t = Timer(30.0, hello, ["world"]) t.start() # after 30 seconds, "hello, world" will be printed ```

In repy use the settimer() function. A repy equivalent would be ```python def hello(str): print "hello," str

t = settimer(30.0, hello, ["world"]) ```

In order to cancel the timer, use python canceltimer(t)

time.time()

In repy you make make use of the getruntime() function. This returns a float representing the runtime of the current program, which is equivalent to the Python: python time.time() - starttime #starttime is when the program started execution

For programs that actually want the "time" (rather than using it to measure elapsed time as most programmers seem to use it), there is a library that does a NTP lookup and provides the correct global time.

Networking

There are several native Repy functions provided to make common networking operations easier. Many don't have direct Python equivalents, but are convenience functions. See the RepyTutorial for examples of these functions.

socket.gethostbyname_ex(name)

In Repy, rather than use [socket.gethostbyname_ex(name)], use gethostbyname_ex(name). The behaviour is the same, so you can write Repy which looks like python gethostbyname_ex("www.google.com")

Threading

threading.Lock()

In Repy use getlock() to create new instances Mutex objects. The object's behaviour is the same in Repy as it is in Python: it supports the acquire and release operations.