9.4. Writing AGI Scripts in
Python
The AGI script we'll be writing in
Python , called "The Subtraction
Game," was inspired by a Perl program written by Ed Guy and
discussed by him at the 2004 AstriCon conference. Ed described his
enthusiasm for the power and simplicity of Asterisk when he found
he could write a quick Perl script to help his young daughter
improve her math skills.
Since we've already written a Perl program using
AGI, and Ed has already written the math program in Perl, we
figured we'd take a stab at it in Python!
Let's go through our Python script.
#!/usr/bin/python
This line tells the system to run this script in
the Python interpreter. For small scripts, you may consider adding
the -u option to this line, which will run Python in
unbuffered mode. This is not recommended, however, for larger or
frequently used AGI scripts, as it can affect system
performance.
import sys
import re
import time
import random
Here, we import several libraries that we'll be
using in our AGI script.
# Read and ignore AGI environment (read until blank line)
env = {}
tests = 0;
while 1:
line = sys.stdin.readline( ).strip( )
if line == '':
break
key,data = line.split(':')
if key[:4] <> 'agi_':
#skip input that doesn't begin with agi_
sys.stderr.write("Did not work!\n");
sys.stderr.flush( )
continue
key = key.strip( )
data = data.strip( )
if key <> '':
env[key] = data
sys.stderr.write("AGI Environment Dump:\n");
sys.stderr.flush( )
for key in env.keys( ):
sys.stderr.write(" -- %s = %s\n" % (key, env[key]))
sys.stderr.flush( )
This section of code reads in the variables that
are passed to our script from Asterisk, and saves them into a
dictionary named env. These values are then written to
STDERR for debugging purposes.
def checkresult (params):
params = params.rstrip( )
if re.search('^200',params):
result = re.search('result=(\d+)',params)
if (not result):
sys.stderr.write("FAIL ('%s')\n" % params)
sys.stderr.flush( )
return -1
else:
result = result.group(1)
#debug("Result:%s Params:%s" % (result, params))
sys.stderr.write("PASS (%s)\n" % result)
sys.stderr.flush( )
return result
else:
sys.stderr.write("FAIL (unexpected result '%s')\n" % params)
sys.stderr.flush( )
return -2
The checkresult function is almost
identical in purpose to the checkresult subroutine in the
sample Perl AGI script we covered earlier in the chapter. It reads
in the result of an Asterisk command, parses the answer, and
reports whether or not the command was successful.
def sayit (params):
sys.stderr.write("STREAM FILE %s \"\"\n" % str(params))
sys.stderr.flush( )
sys.stdout.write("STREAM FILE %s \"\"\n" % str(params))
sys.stdout.flush( )
result = sys.stdin.readline( ).strip( )
checkresult(result)
The sayit function is a simple wrapper
around the STREAM FILE command.
def saynumber (params):
sys.stderr.write("SAY NUMBER %s \"\"\n" % params)
sys.stderr.flush( )
sys.stdout.write("SAY NUMBER %s \"\"\n" % params)
sys.stdout.flush( )
result = sys.stdin.readline( ).strip( )
checkresult(result)
The saynumber function is a simple
wrapper around the SAY NUMBER command.
def getnumber (prompt, timelimit, digcount):
sys.stderr.write("GET DATA %s %d %d\n" % (prompt, timelimit, digcount))
sys.stderr.flush( )
sys.stdout.write("GET DATA %s %d %d\n" % (prompt, timelimit, digcount))
sys.stdout.flush( )
result = sys.stdin.readline( ).strip( )
result = checkresult(result)
sys.stderr.write("digits are %s\n" % result)
sys.stderr.flush( )
if result:
return result
else:
result = -1
The getnumber function calls the
GET DATA command to get DTMF input from the caller. It is
used in our program to get the caller's answers to the subtraction
problems.
limit=20
digitcount=2
score=0
count=0
ttanswer=5000
Here, we initialize a few variables that we'll
be using in our program.
starttime = time.time( )
t = time.time( ) - starttime
In these lines we set the starttime
variable to the current time and initialize t to zero.
We'll use the t variable to keep track of the number of
seconds that have elapsed since the AGI script was started.
sayit("subtraction-game-welcome")
Next, we welcome the caller to the subtraction
game.
while ( t < 180 ):
big = random.randint(0,limit+1)
big += 10
subt= random.randint(0,big)
ans = big - subt
count += 1
#give problem:
sayit("subtraction-game-next");
saynumber(big);
sayit("minus");
saynumber(subt);
res = getnumber("equals",ttanswer,digitcount);
if (int(res) == ans) :
score+=1
sayit("subtraction-game-good");
else :
sayit("subtraction-game-wrong");
saynumber(ans);
t = time.time( ) - starttime
This is the heart of the AGI script. We loop
through this section of code and give subtraction problems to the
caller until 180 seconds have elapsed. Near the top of the loop, we
calculate two random numbers and their difference. We then present
the problem to the caller, and read in the caller's response. If
the caller answers incorrectly, we give the correct answer.
pct = float(score)/float(count)*100;
sys.stderr.write("Percentage correct is %d\n" % pct)
sys.stderr.flush( )
sayit("subtraction-game-timesup")
saynumber(score)
sayit("subtraction-game-right")
saynumber(count)
sayit("subtraction-game-pct")
saynumber(pct)
After the users are done answering the
subtraction problems, they are given their scores.
As you have seen, the basics you should remember
when writing AGI scripts in Python are:
-
Flush the output buffer after every write. This
will ensure that your AGI program won't hang while Asterisk is
waiting for the buffer to fill and Python is waiting for the
response from Asterisk.
-
Read data from Asterisk with the
sys.stdin.readline command.
-
Write commands to Asterisk with the
sys.stdout.write command. Don't forget to call
sys.stdout.flush after writing.
9.4.1. The Python AGI Library
If you are planning on writing lot of Python AGI
code, you may want to check out Karl Putland's Python module,
Pyst. You can find it at http://www.sourceforge.net/projects/pyst/. |
