# Tutorial

This tutorial will explain a couple of basic Pyro concepts, a little bit about the name server, and you’ll learn to write a simple Pyro application. You’ll do this by writing a warehouse system and a stock market simulator, that demonstrate some key Pyro techniques.

## Warm-up

Before proceeding, you should install Pyro if you haven’t done so. For instructions about that, see Installing Pyro.

In this tutorial, you will use Pyro’s default configuration settings, so once Pyro is installed, you’re all set! All you need is a text editor and a couple of console windows. During the tutorial, you are supposed to run everything on a single machine. This avoids initial networking complexity.

Note

For security reasons, Pyro runs stuff on localhost by default. If you want to access things from different machines, you’ll have to tell Pyro to do that explicitly. At the end is a small section phase 3: running it on different machines that tells you how you can run the various components on different machines.

Note

The code of the two tutorial ‘projects’ is included in the Pyro source archive. Just installing Pyro won’t provide this. If you don’t want to type all the code, you should extract the Pyro source archive (`Pyro4-X.Y.tar.gz`) somewhere. You will then have an `examples` directory that contains a truckload of examples, including the two tutorial projects we will be creating later in this tutorial, `warehouse` and `stockquotes`. (There is more in there as well: the `tests` directory contains the test suite with all the unittests for Pyro’s code base.)

## Pyro concepts and tools

Pyro enables code to call methods on objects even if that object is running on a remote machine:

    +----------+                         +----------+
    | server A |                         | server B |
    |          |       < network >       |          |
    | Python   |                         |   Python |
    | OBJECT ----------foo.invoke()--------> OBJECT |
    |          |                         |     foo  |
    +----------+                         +----------+

Pyro is mainly used as a library in your code but it also has several supporting command line tools [1]. We won’t explain every one of them here as you will only need the “name server” for this tutorial.

[1] | Actually there are no scripts or command files included with Pyro right now. The Command line tools are invoked by starting their package directly using the `-m` argument of the Python interpreter.

### Key concepts

Here are a couple of key concepts you encounter when using Pyro:

Proxy
  A proxy is a substitute object for “the real thing”. It intercepts the method calls you would normally do on an object as if it was the actual object. Pyro then performs some magic to transfer the call to the computer that contains the real object, where the actual method call is done, and the results are returned to the caller. This means the calling code doesn’t have to know if it’s dealing with a normal or a remote object, because the code is identical. The class implementing Pyro proxies is `Pyro4.Proxy` (shortcut for `Pyro4.core.Proxy`)
URI
  This is what Pyro uses to identify every object. (similar to what a web page URL is to point to the different documents on the web). Its string form is like this: “PYRO:” + object name + “@” + server name + port number. There are a few other forms it can take as well. You can write the protocol in lowercase too if you want (“pyro:”) but it will automatically be converted to uppercase internally. The class implementing Pyro uris is `Pyro4.URI` (shortcut for `Pyro4.core.URI`)
Pyro object
  This is a normal Python object but it is registered with Pyro so that you can access it remotely. Pyro objects are written just as any other object but the fact that Pyro knows something about them makes them special, in the way that you can call methods on them from other programs. A class can also be a Pyro object, but then you will also have to tell Pyro about how it should create actual objects from that class when handling remote calls.
Pyro daemon (server)
  This is the part of Pyro that listens for remote method calls, dispatches them to the appropriate actual objects, and returns the results to the caller. All Pyro objects are registered in one or more daemons.
Pyro name server
  The name server is a utility that provides a phone book for Pyro applications: you use it to look up a “number” by a “name”. The name in Pyro’s case is the logical name of a remote object. The number is the exact location where Pyro can contact the object. Usually there is just one name server running in your network.
Serialization
  This is the process of transforming objects into streams of bytes that can be transported over the network. The receiver deserializes them back into actual objects. Pyro needs to do this with all the data that is passed as arguments to remote method calls, and their response data. Not all objects can be serialized, so it is possible that passing a certain object to Pyro won’t work even though a normal method call would accept it just fine.
Configuration
  Pyro can be configured in a lot of ways. Using environment variables (they’re prefixed with `PYRO_`) or by setting config items in your code. See the configuration chapter for more details. The default configuration should be ok for most situations though, so you many never have to touch any of these options at all!

### Starting a name server

While the use of the Pyro name server is optional, we will use it in this tutorial. It also shows a few basic Pyro concepts, so let us begin by explaining a little about it. Open a console window and execute the following command to start a name server:

python -m Pyro4.naming (or simply: pyro4-ns)

The name server will start and it prints something like:

    Not starting broadcast server for localhost.
    NS running on localhost:9090 (127.0.0.1)
    URI = PYRO:Pyro.NameServer@localhost:9090

The name server has started and is listening on localhost port 9090.

It also printed an URI. Remember that this is what Pyro uses to identify every object.

The name server can be stopped with a `control-c`, or on Windows, with `ctrl-break`. But let it run in the background for the rest of this tutorial.

### Interacting with the name server

There’s another command line tool that let you interact with the name server: “nsc” (name server control tool). You can use it, amongst other things, to see what all known registered objects in the naming server are. Let’s do that right now. Type:

python -m Pyro4.nsc list (or simply: pyro4-nsc list)

and it will print something like this:

    --------START LIST
    Pyro.NameServer --> PYRO:Pyro.NameServer@localhost:9090
    --------END LIST

The only object that is currently registered, is the name server itself! (Yes, the name server is a Pyro object itself. Pyro and the “nsc” tool are using Pyro to talk to it).

Note

As you can see, the name `Pyro.NameServer` is registered to point to the URI that we saw earlier. This is mainly for completeness sake, and is not often used, because there are different ways to get to talk to the name server (see below).

This is cool, but there’s a little detail left unexplained: How did the nsc tool know where the name server was? Pyro has a couple of tactics to locate a name server. The nsc tool uses them too: Pyro uses a network broadcast to see if there’s a name server available somewhere (the name server contains a broadcast responder that will respond “Yeah hi I’m here”). So in many cases you won’t have to configure anything to be able to discover the name server. If nobody answers though, Pyro tries the configured default or custom location. If still nobody answers it prints a sad message and exits. However if it found the name server, it is then possible to talk to it and get the location of any other registered object. This means that you won’t have to hard code any object locations in your code, and that the code is capable of dynamically discovering everything at runtime.

But enough of that. We need to start looking at how to actually write some code ourselves that uses Pyro!

## Building a Warehouse

Hint

All code of this part of the tutorial can be found in the `examples/warehouse` directory.

You’ll build a simple warehouse that stores items, and that everyone can visit. Visitors can store items and retrieve other items from the warehouse (if they’ve been stored there).

In this tutorial you’ll first write a normal Python program that more or less implements the complete warehouse system, but in vanilla Python code. After that you’ll add Pyro support to it, to make it a distributed warehouse system, where you can visit the central warehouse from many different computers.

### phase 1: a simple prototype

To start with, write the vanilla Python code for the warehouse and its visitors. This prototype is fully working but everything is running in a single process. It contains no Pyro code at all, but shows what the system is going to look like later on.

The `Warehouse` object simply stores an array of items which we can query, and allows for a person to take an item or to store an item. Here is the code (`warehouse.py`):

    from __future__ import print_function

    class Warehouse(object):
        def __init__(self):
            self.contents = ["chair", "bike", "flashlight", "laptop", "couch"]

        def list_contents(self):
            return self.contents

        def take(self, name, item):
            self.contents.remove(item)
            print("{0} took the {1}.".format(name, item))

        def store(self, name, item):
            self.contents.append(item)
            print("{0} stored the {1}.".format(name, item))

Then there is a `Person` that can visit the warehouse. The person has a name and deposit and retrieve actions on a particular warehouse. Here is the code (`person.py`):

    from __future__ import print_function
    import sys

    if sys.version_info < (3, 0):
        input = raw_input

    class Person(object):
        def __init__(self, name):
            self.name = name

        def visit(self, warehouse):
            print("This is {0}.".format(self.name))
            self.deposit(warehouse)
            self.retrieve(warehouse)
            print("Thank you, come again!")

        def deposit(self, warehouse):
            print("The warehouse contains:", warehouse.list_contents())
            item = input("Type a thing you want to store (or empty): ").strip()
            if item:
                warehouse.store(self.name, item)

        def retrieve(self, warehouse):
            print("The warehouse contains:", warehouse.list_contents())
            item = input("Type something you want to take (or empty): ").strip()
            if item:
                warehouse.take(self.name, item)

Finally you need a small script that actually runs the code. It creates the warehouse and two visitors, and makes the visitors perform their actions in the warehouse. Here is the code (`visit.py`):

    # This is the code that runs this example.
    from warehouse import Warehouse
    from person import Person

    warehouse = Warehouse()
    janet = Person("Janet")
    henry = Person("Henry")
    janet.visit(warehouse)
    henry.visit(warehouse)

Run this simple program. It will output something like this:

    $ python visit.py
    This is Janet.
    The warehouse contains: ['chair', 'bike', 'flashlight', 'laptop', 'couch']
    Type a thing you want to store (or empty): television   # typed in
    Janet stored the television.
    The warehouse contains: ['chair', 'bike', 'flashlight', 'laptop', 'couch', 'television']
    Type something you want to take (or empty): couch    # <-- typed in
    Janet took the couch.
    Thank you, come again!
    This is Henry.
    The warehouse contains: ['chair', 'bike', 'flashlight', 'laptop', 'television']
    Type a thing you want to store (or empty): bricks   # <-- typed in
    Henry stored the bricks.
    The warehouse contains: ['chair', 'bike', 'flashlight', 'laptop', 'television', 'bricks']
    Type something you want to take (or empty): bike   # <-- typed in
    Henry took the bike.
    Thank you, come again!

### phase 2: first Pyro version

That wasn’t very exciting but you now have working code for the basics of the warehouse system. Now you’ll use Pyro to turn the warehouse into a standalone component, that people from other computers can visit. You’ll need to add a couple of lines to the `warehouse.py` file so that it will start a Pyro server for the warehouse object. You can do this by registering your Pyro class with a ‘Pyro daemon’, the server that listens for and processes incoming remote method calls. One way to do that is like this (you can ignore the details about this for now):

    Pyro4.Daemon.serveSimple(
            {
                Warehouse: "example.warehouse"
            },
            ns = False)

Next, we have to tell Pyro what parts of the class should be remotely accessible, and what parts aren’t supposed to be accessible. This has to do with security. We’ll be adding a `@Pyro4.expose` decorator on the Warehouse class definition to tell Pyro it is allowed to access the class remotely. You can ignore the `@Pyro4.behavior` line we also added for now (but it is required to properly have a persistent warehouse inventory). Finally we add a little `main` function so it will be started correctly, which should make the code now look like this (`warehouse.py`):

    from __future__ import print_function
    import Pyro4

    @Pyro4.expose
    @Pyro4.behavior(instance_mode="single")
    class Warehouse(object):
        def __init__(self):
            self.contents = ["chair", "bike", "flashlight", "laptop", "couch"]

        def list_contents(self):
            return self.contents

        def take(self, name, item):
            self.contents.remove(item)
            print("{0} took the {1}.".format(name, item))

        def store(self, name, item):
            self.contents.append(item)
            print("{0} stored the {1}.".format(name, item))

    def main():
        Pyro4.Daemon.serveSimple(
                {
                    Warehouse: "example.warehouse"
                },
                ns = False)

    if __name__=="__main__":
        main()

Start the warehouse in a new console window, it will print something like this:

    $ python warehouse.py
    Object <__main__.Warehouse object at 0x025F4FF0>:
        uri = PYRO:example.warehouse@localhost:51279
    Pyro daemon running.

It will become clear what you need to do with this output in a second. You now need to slightly change the `visit.py` script that runs the thing. Instead of creating a warehouse directly and letting the persons visit that, it is going to use Pyro to connect to the stand alone warehouse object that you started above. It needs to know the location of the warehouse object before it can connect to it. This is the uri that is printed by the warehouse program above (`PYRO:example.warehouse@localhost:51279`). You’ll need to ask the user to enter that uri string into the program, and use Pyro to create a proxy to the remote object:

    uri = input("Enter the uri of the warehouse: ").strip()
    warehouse = Pyro4.Proxy(uri)

That is all you need to change. Pyro will transparently forward the calls you make on the warehouse object to the remote object, and return the results to your code. So the code will now look like this (`visit.py`):

    # This is the code that visits the warehouse.
    import sys
    import Pyro4
    from person import Person

    if sys.version_info<(3,0):
        input = raw_input

    uri = input("Enter the uri of the warehouse: ").strip()
    warehouse = Pyro4.Proxy(uri)
    janet = Person("Janet")
    henry = Person("Henry")
    janet.visit(warehouse)
    henry.visit(warehouse)

Notice that the code of `Warehouse` and `Person` classes didn’t change at all.

Run the program. It will output something like this:

    $ python visit.py
    Enter the uri of the warehouse: PYRO:example.warehouse@localhost:51279  # copied from warehouse output
    This is Janet.
    The warehouse contains: ['chair', 'bike', 'flashlight', 'laptop', 'couch']
    Type a thing you want to store (or empty): television   # typed in
    The warehouse contains: ['chair', 'bike', 'flashlight', 'laptop', 'couch', 'television']
    Type something you want to take (or empty): couch   # <-- typed in
    Thank you, come again!
    This is Henry.
    The warehouse contains: ['chair', 'bike', 'flashlight', 'laptop', 'television']
    Type a thing you want to store (or empty): bricks   # <-- typed in
    The warehouse contains: ['chair', 'bike', 'flashlight', 'laptop', 'television', 'bricks']
    Type something you want to take (or empty): bike    # <-- typed in
    Thank you, come again!

And notice that in the other console window, where the warehouse server is running, the following is printed:

    Janet stored the television.
    Janet took the couch.
    Henry stored the bricks.
    Henry took the bike.

### phase 3: final Pyro version

The code from the previous phase works fine and could be considered to be the final program, but is a bit cumbersome because you need to copy-paste the warehouse URI all the time to be able to use it. You will simplify it a bit in this phase by using the Pyro name server. Also, you will use the Pyro excepthook to print a nicer exception message if anything goes wrong (by taking something from the warehouse that is not present! Try that now with the code from phase 2. You will get a `ValueError: list.remove(x): x not in list` but with a not so useful stack trace).

Note

Once again you can leave code of the `Warehouse` and `Person` classes unchanged. As you can see, Pyro is not getting in your way at all here. You can often use it with only adding a couple of lines to your existing code.

Okay, stop the warehouse program from phase 2 if it is still running, and check if the name server that you started in Starting a name server is still running in its own console window.

In `warehouse.py` locate the statement `Pyro4.Daemon.serveSimple(...` and change the `ns = False` argument to `ns = True`. This tells Pyro to use a name server to register the objects in. (The `Pyro4.Daemon.serveSimple` is a very easy way to start a Pyro server but it provides very little control. Look here Oneliner Pyro object publishing: serveSimple() for some more details, and you will learn about another way of starting a server in Building a Stock market simulator).

In `visit.py` remove the input statement that asks for the warehouse uri, and change the way the warehouse proxy is created. Because you are now using a name server you can ask Pyro to locate the warehouse object automatically:

    warehouse = Pyro4.Proxy("PYRONAME:example.warehouse")

Finally, install the `Pyro4.util.excepthook` as excepthook. You’ll soon see what this does to the exceptions and stack traces your program produces when something goes wrong with a Pyro object. So the code should look something like this (`visit.py`):

    # This is the code that visits the warehouse.
    import sys
    import Pyro4
    import Pyro4.util
    from person import Person

    sys.excepthook = Pyro4.util.excepthook

    warehouse = Pyro4.Proxy("PYRONAME:example.warehouse")
    janet = Person("Janet")
    henry = Person("Henry")
    janet.visit(warehouse)
    henry.visit(warehouse)

Start the warehouse program again in a separate console window. It will print something like this:

    $ python warehouse.py
    Object <__main__.Warehouse object at 0x02496050>:
        uri = PYRO:obj_426e82eea7534fb5bc78df0b5c0b6a04@localhost:51294
        name = example.warehouse
    Pyro daemon running.

As you can see the uri is different this time, it now contains some random id code instead of a name. However it also printed an object name. This is the name that is now used in the name server for your warehouse object. Check this with the ‘nsc’ tool: python -m Pyro4.nsc list (or simply: pyro4-nsc list), which will print something like:

    --------START LIST
    Pyro.NameServer --> PYRO:Pyro.NameServer@localhost:9090
    example.warehouse --> PYRO:obj_426e82eea7534fb5bc78df0b5c0b6a04@localhost:51294
    --------END LIST

This means you can now refer to that warehouse object using the name `example.warehouse` and Pyro will locate the correct object for you automatically. This is what you changed in the `visit.py` code so run that now to see that it indeed works!

Remote exception: You also installed Pyro’s custom excepthook so try that out. Run the `visit.py` script and try to take something from the warehouse that is not present (for instance, batteries):

    Type something you want to take (or empty): batteries
    Traceback (most recent call last):
      File "visit.py", line 12, in <module>
        janet.visit(warehouse)
      File "d:\PROJECTS\Pyro4\examples\warehouse\phase3\person.py", line 14, in visit
        self.retrieve(warehouse)
      File "d:\PROJECTS\Pyro4\examples\warehouse\phase3\person.py", line 25, in retrieve
        warehouse.take(self.name, item)
      File "d:\PROJECTS\Pyro4\src\Pyro4\core.py", line 161, in __call__
        return self.__send(self.__name, args, kwargs)
      File "d:\PROJECTS\Pyro4\src\Pyro4\core.py", line 314, in _pyroInvoke
        raise data
    ValueError: list.remove(x): x not in list
     +--- This exception occured remotely (Pyro) - Remote traceback:
     | Traceback (most recent call last):
     |   File "d:\PROJECTS\Pyro4\src\Pyro4\core.py", line 824, in handleRequest
     |     data=method(*vargs, **kwargs)   # this is the actual method call to the Pyro object
     |   File "warehouse.py", line 14, in take
     |     self.contents.remove(item)
     | ValueError: list.remove(x): x not in list
     +--- End of remote traceback

What you can see now is that you not only get the usual exception traceback, but also the exception that occurred in the remote warehouse object on the server (the “remote traceback”). This can greatly help locating problems! As you can see it contains the source code lines from the warehouse code that is running in the server, as opposed to the normal local traceback that only shows the remote method call taking place inside Pyro.

## Building a Stock market simulator

Hint

All of the code of this part of the tutorial can be found in the `examples/stockquotes` directory.

We’ll build a simple stock quote system. The idea is that we have multiple stock markets producing stock symbol quotes. There are viewers that aggregate and filter all stock quotes from the markets and display those from the companies we are interested in.

Stockmarket 1 | → |  | Viewer
Stockmarket 2 | → | → | Viewer
Stockmarket 3 | → |  | Viewer
… |  |  | …

### phase 1: simple prototype

Again, like the previous application (the warehouse), you first create a working version of the system by only using normal Python code. This simple prototype will be functional but everything will be running in a single process. It contains no Pyro code at all, but shows what the system is going to look like later on.

First create a file `stockmarket.py` that will simulate a stock market that is producing stock quotes for registered companies. For simplicity we will use a generator function that produces individual random stock quotes. The code is as follows:

    # stockmarket.py
    import random
    import time

    class StockMarket(object):
        def __init__(self, marketname, symbols):
            self.name = marketname
            self.symbols = symbols

        def quotes(self):
            while True:
                symbol = random.choice(self.symbols)
                yield symbol, round(random.uniform(5, 150), 2)
                time.sleep(random.random()/2.0)

For the actual viewer application we create a new file `viewer.py` that iterates over the symbols produced by various stock markets. It prints the symbols from the companies we’re interested in:

    # viewer.py
    from __future__ import print_function
    from stockmarket import StockMarket

    class Viewer(object):
        def __init__(self):
            self.markets = set()
            self.symbols = set()

        def start(self):
            print("Shown quotes:", self.symbols)
            quote_sources = {
                market.name: market.quotes() for market in self.markets
            }
            while True:
                for market, quote_source in quote_sources.items():
                    quote = next(quote_source)  # get a new stock quote from the source
                    symbol, value = quote
                    if symbol in self.symbols:
                        print("{0}.{1}: {2}".format(market, symbol, value))

    def main():
        nasdaq = StockMarket("NASDAQ", ["AAPL", "CSCO", "MSFT", "GOOG"])
        newyork = StockMarket("NYSE", ["IBM", "HPQ", "BP"])
        viewer = Viewer()
        viewer.markets = {nasdaq, newyork}
        viewer.symbols = {"IBM", "AAPL", "MSFT"}
        viewer.start()

    if __name__ == "__main__":
        main()

If you run this file `viewer.py` it will print a stream of stock symbol quote updates that are being generated by the two stock markets (but only the few symbols that the viewer wants to see):

    $ python viewer.py
    Shown quotes: {'MSFT', 'IBM', 'AAPL'}
    NYSE.IBM: 19.59
    NASDAQ.MSFT: 25.06
    NYSE.IBM: 89.54
    NYSE.IBM: 44.08
    NASDAQ.MSFT: 9.73
    NYSE.IBM: 80.57
    ....

### phase 2: Pyro version

Now you use Pyro to make the various components fully distributed. Pyro is used to make them talk to each other. The actual code for each component class hasn’t really changed since phase 1, it is just the plumbing that you need to write to glue them together. Pyro is making this a matter of just a few lines of code that is Pyro-specific, the rest of the code is needed anyway to start up and configure the system. To be able to see the final result, the code is listed once more with comments on what changed with respect to the version in phase 1.

#### stockmarket

The `stockmarket.py` is changed slightly. You have to add the `@Pyro4.expose` decorator on the methods (or class) that must be accessible remotely. Also, to access the `name` and `symbols` attributes of the class you have to turn them into real Python properties. Finally there is now a bit of startup logic to create some stock markets and make them available as Pyro objects. Notice that we gave each market their own defined name, this will be used in the viewer application later.

For sake of example we are not using the `serveSimple` method here to publish our objects via Pyro. Rather, the daemon and name server are accessed by our own code. Notice that to ensure tidy cleanup of connectoin resources, they are both used as context managers in a `with` statement.

Also notice that we can leave the generator function in the stockmarket class as-is; since version 4.49 Pyro is able to turn it into a remote generator without your client program ever noticing.

The complete code for the Pyro version of `stockmarket.py` is as follows:

    # stockmarket.py
    from __future__ import print_function
    import random
    import time
    import Pyro4

    @Pyro4.expose
    class StockMarket(object):
        def __init__(self, marketname, symbols):
            self._name = marketname
            self._symbols = symbols

        def quotes(self):
            while True:
                symbol = random.choice(self.symbols)
                yield symbol, round(random.uniform(5, 150), 2)
                time.sleep(random.random()/2.0)

        @property
        def name(self):
            return self._name

        @property
        def symbols(self):
            return self._symbols

    if __name__ == "__main__":
        nasdaq = StockMarket("NASDAQ", ["AAPL", "CSCO", "MSFT", "GOOG"])
        newyork = StockMarket("NYSE", ["IBM", "HPQ", "BP"])
        # for example purposes we will access the daemon and name server ourselves and not use serveSimple
        with Pyro4.Daemon() as daemon:
            nasdaq_uri = daemon.register(nasdaq)
            newyork_uri = daemon.register(newyork)
            with Pyro4.locateNS() as ns:
                ns.register("example.stockmarket.nasdaq", nasdaq_uri)
                ns.register("example.stockmarket.newyork", newyork_uri)
            print("Stockmarkets available.")
            daemon.requestLoop()

#### viewer

You don’t need to change the actual code in the `Viewer`, other than how to tell it what stock market objects it should use. Rather than hard coding the fixed set of stockmarket names, it is more flexible to utilize Pyro’s name server and ask that to return all stock markets it knows about. The `Viewer` class itself remains unchanged:

    # viewer.py
    from __future__ import print_function
    import Pyro4

    class Viewer(object):
        def __init__(self):
            self.markets = set()
            self.symbols = set()

        def start(self):
            print("Shown quotes:", self.symbols)
            quote_sources = {
                market.name: market.quotes() for market in self.markets
            }
            while True:
                for market, quote_source in quote_sources.items():
                    quote = next(quote_source)  # get a new stock quote from the source
                    symbol, value = quote
                    if symbol in self.symbols:
                        print("{0}.{1}: {2}".format(market, symbol, value))

    def find_stockmarkets():
        # You can hardcode the stockmarket names for nasdaq and newyork, but it
        # is more flexible if we just look for every available stockmarket.
        markets = []
        with Pyro4.locateNS() as ns:
            for market, market_uri in ns.list(prefix="example.stockmarket.").items():
                print("found market", market)
                markets.append(Pyro4.Proxy(market_uri))
        if not markets:
            raise ValueError("no markets found! (have you started the stock markets first?)")
        return markets

    def main():
        viewer = Viewer()
        viewer.markets = find_stockmarkets()
        viewer.symbols = {"IBM", "AAPL", "MSFT"}
        viewer.start()

    if __name__ == "__main__":
        main()

#### running the program

To run the final stock quote system you need to do the following:

- open a new console window and start the Pyro name server (python -m Pyro4.naming, or simply: pyro4-ns).
- open another console window and start the stock market server
- open another console window and start the viewer

The stock market program doesn’t print much by itself but it sends stock quotes to the viewer, which prints them:

    $ python viewer.py
    found market example.stockmarket.newyork
    found market example.stockmarket.nasdaq
    Shown quotes: {'AAPL', 'IBM', 'MSFT'}
    NASDAQ.AAPL: 82.58
    NYSE.IBM: 85.22
    NYSE.IBM: 124.68
    NASDAQ.AAPL: 88.55
    NYSE.IBM: 40.97
    NASDAQ.MSFT: 38.83
    ...

If you’re interested to see what the name server now contains, type python -m Pyro4.nsc list (or simply: pyro4-nsc list):

    $ pyro4-nsc list
    --------START LIST
    Pyro.NameServer --> PYRO:Pyro.NameServer@localhost:9090
        metadata: ['class:Pyro4.naming.NameServer']
    example.stockmarket.nasdaq --> PYRO:obj_3896de2eb38b4bed9d12ba91703539a4@localhost:51479
    example.stockmarket.newyork --> PYRO:obj_1ab1a322e5c14f9e984a0065cd080f56@localhost:51479
    --------END LIST

### phase 3: running it on different machines

Before presenting the changes in phase 3, let’s introduce some additional notions when working with Pyro.

It’s important for you to understand that, for security reasons, Pyro runs stuff on localhost by default. If you want to access things from different machines, you’ll have to tell Pyro to do that explicitly. Here we show you how you can do this:

Let’s assume that you want to start the name server in such a way that it is accessible from other machines. To do that, type in the console one of two options (with an appropriate -n argument):

> $ python -m Pyro4.naming -n your_hostname # i.e. your_hostname = “192.168.1.99”

or simply:

> $ pyro4-ns -n your_hostname

If you want to implement this concept on the warehouse server, you’ll have to modify `warehouse.py`. Then, right before the `serveSimple` call, you have to tell it to bind the daemon on your hostname instead of localhost. One way to do this is by setting the `HOST` config item:

    Pyro4.config.HOST = "your_hostname_here"
    Pyro4.Daemon.serveSimple(...)

Optionally, you can choose to leave the code alone, and instead set the `PYRO_HOST` environment variable before starting the warehouse server. Another choice is to pass the required host (and perhaps even port) arguments to `serveSimple`:

    Pyro4.Daemon.serveSimple(
            {
                Warehouse: "example.warehouse"
            },
            host = 'your_hostname_here',
            ns = True)

Remember that if you want more details, refer to the chapters in this manual about the relevant Pyro components.

Now, back on the new version of the stock market server, notice that this example already creates a daemon object instead of using the `serveSimple()` call. You’ll have to modify `stockmarket.py` because that is the one creating a daemon. But you’ll only have to add the proper `host``and ``port` arguments to the construction of the Daemon, to set it to your machine name instead of the default of localhost. Let’s see the few minor changes that are required in the code:

> … HOST_IP = “192.168.1.99” HOST_PORT = 9092 … with Pyro4.Daemon(host=HOST_IP, port=HOST_PORT) as daemon: …

Of course, you could also change the `HOST` config item (either in the code itself, or by setting the `PYRO_HOST` environment variable before launching).

## Other means of creating connections

In both tutorials above we used the Name Server for easy object lookup. The use of the name server is optional, see Name Server for details. There are various other options for connecting your client code to your Pyro objects, have a look at the client code details: Object discovery and the server code details: Pyro Daemon: publishing Pyro objects.

## Ok, what’s next?

Congratulations! You completed the Pyro tutorials in which you built a simple warehouse storage system, and a stock market simulation system consisting of various independent components that talk to each other using Pyro. The Pyro distribution archive contains a truckload of example programs with short descriptions that you could study to see how to use the various features that Pyro has to offer. Or just browse the manual for more detailed information. Happy remote object programming!