I have the following piece of code, taken from a bigger module, that
even as I was writing I _knew_ there were better ways of doing it, using
a parser or somesuch at least, but learning how wasn't as fun as coding
it... And yes alarm bells went off when I found myself typing eval(),
and I'm sure this is an 'unusual' use of for: else: . And I know it's
not very robust. As an ex cuse/planation, this is what happens when you
get an idea in your head and code it until it works, rather than doing
any kind of planning / designing first :)
I have a file that indicates the syntax of commands. User input is
checked against this file until it matches one of the lines in the file.
Then the indicated commands are run.
I think what I have ended up doing is writing a kind of a brute-force
parser for the file format I have defined. The trouble is, I'm sure
there are much more 'agile' and 'elegant' ways of achieveing this, and
also getting rid of eval() !
I'm posting here in the hope that it will criticised, laughed at, picked
apart and hence I shall learn a bit about python and how to do this
properly :)
The code follows, followed by the file defining the syntax of commands.
import re
def dbg(Msg,Fn):
try:
if (TRACE[Fn] or TRACE["ALL"]):
print 'DBG:'+Fn+': '+Msg
except KeyError:
pass
def processsubstitutions(RawCmd):
DBGBN='processsubstitutions'
infprotect=1
subhit=1
while subhit==1:
subhit=0
for sub in Substitutions:
SubCheck=RawCmd
RawCmd=re.sub('~'+sub,' '.join(Substitutions[sub]),RawCmd)
if SubCheck!=RawCmd:
#dbg('Made Substitution '+sub+' to get '+RawCmd,DBGBN)
subhit=1
infprotect=infprotect+1
if infprotect>100:
return "ERROR: Infinitely deep substitution levels
detected."
return RawCmd
#
#...processcommand is called with a string entered by the user.
#
def processcommand(Command):
DBGBN='processcommand'
dbg('Before Substitution: '+Command,DBGBN)
Command=processsubstitutions(Command) # if ! aliascmd then flow
is, RawCmd->subbed->executed
# is IS aliascmd
then flow is RawCmd->Subbed->aliashit->subbed->executed
dbg('After Substitution: '+Command,DBGBN)
AliasHit=0
CommandHit=0
SplitCmd=Command.split()
SplitLen=len(SplitCmd)
Cmd=SplitCmd[0]
InEtcRun=0
Error=0
CommandDefs=file(installroot+'FatControllerCommands.sav','r')
for Def in CommandDefs:
dbg("Scanning cdef ::"+Def,DBGBN)
if Def!='ENDCOMMANDDEFS':
DefTokens=Def.split()
ctr=0
for Token in DefTokens:
dbg("Doing token "+Token,DBGBN)
if re.search('input:',Token):
if SplitLen>ctr:
dbg("Is an input tag. ValExp=",DBGBN)
ValidateExpression=Token.replace('input:','').replace('<<',SplitCmd[ctr]
).replace('::SPACE::',' ')
dbg(ValidateExpression,DBGBN)
else:
Error=1
ErrorText='Error: Missing parameter.'
break
if not eval(ValidateExpression):##NOT SAFE NOT SAFE.
Need to come up with entirely new
##way to do all this
Error=1
ErrorText='Error: Parameter incorrect.'
break
elif re.search('create:',Token):
CreateExpression=Token.replace('create:','').replace('::SPACE::',' ')
elif Token!='+*':
if ctr>=SplitLen:
Error=1
ErrorText='Error: Bad command.'
break
if Token!=SplitCmd[ctr]:
Error=1
ErrorText='Error: Bad command.'
break
ctr+=1
CommandHit=1
else: #{EndOf for Token} all tokens found for else
eval(CreateExpression)
break
else: #{EndOf for Def} Check aliases
for AliasName in Aliases:
if Cmd==AliasName: #then, make cmdstring alias cmd string
and re-process
AliasCmd=' '.join(Aliases[AliasName])
AliasHit=1
dbg('Made alias hit to get '+AliasCmd,DBGBN)
break
else: #FOR loop else not an alias, so try execute as last
entity command
if not CommandHit:
global LastExecutedEntity
if LastExecutedEntity!='':
#global LastExecutedEntity
EntityManager.execute(LastExecutedEntity,SplitCmd[0:])
else:
print '\nError: Dont know which entity to use.\n'
else:
print '\nError: Bad command.\n'
if AliasHit==1:
AliasHit=0
CommandDefs.close()
processcommand(AliasCmd)
CommandDefs.close()
.....now the file. First I will explain what is in it;
The 'grammar'? Or file format I have defined is as follows. The aim is
to specify the syntax of commands that are then checked against user
input until a match is found, then eval() is used to call the function
given in the file. (bad I know)
There are sveral tokens in the file, this is what they mean
Input:(some condition, possibly containing '<<') - Whatever the user
has entered in this field replaces '<<' the resulting code must eval to
True.
Create:(function call using SplitCmd[]) - eval is used if
user input has matched the line to make the given function call,
SplitCmd is a list of the lines values.
+* indicates the user could enter any number of any parms , these are
handled by the code executed via the create: token.
....simple huh?
Here's the file 'FatControllerCommands.sav' (some lines are long, turn
off wrapping):
alias input:'<<'!='' +* create:definealias(SplitCmd[1],SplitCmd[2:])
define entity input:not(EntityManager.isEntity('<<')) input:'<<'!='' +*
create:EntityManager.define(SplitCmd[2],SplitCmd[3:])
def entity input:not(EntityManager.isEntity('<<')) input:'<<'!='' +*
create:EntityManager.define(SplitCmd[2],SplitCmd[3:])
delete entity input:EntityManager.isEntity('<<')
create:EntityManager.delete(SplitCmd[2])
del entity input:EntityManager.isEntity('<<')
create:EntityManager.delete(SplitCmd[2])
delete alias input:isalias('<<') create:delalias(SplitCmd[2])
del alias input:isalias('<<') create:delalias(SplitCmd[2])
delete substitution input:issubstitute('<<')
create:delsubstitution(SplitCmd[2])
delete sub input:issubstitute('<<') create:delsubstitution(SplitCmd[2])
del substitution input:issubstitute('<<')
create:delsubstitution(SplitCmd[2])
del sub input:issubstitute('<<') create:delsubstitution(SplitCmd[2])
execute input:EntityManager.isEntity('<<') input:'<<'!='' +*
create:EntityManager.execute(SplitCmd[1],SplitCmd[2:])
exec input:EntityManager.isEntity('<<') input:'<<'!='' +*
create:EntityManager.execute(SplitCmd[1],SplitCmd[2:])
x input:EntityManager.isEntity('<<') input:'<<'!='' +*
create:EntityManager.execute(SplitCmd[1],SplitCmd[2:])
exit create:sys.exit(0)
quit create:sys.exit(0)
help create:displayhelp()
load input:'<<'!='' create:load(SplitCmd[1])
save input:'<<'==('all') input:not(00)
create:save(SplitCmd[1],SplitCmd[2])
show entities create:EntityManager.show()
show aliases create:showaliases()
show substitutions create:showsubstitutions()
show subs create:showsubstitutions()
show daemons create:showdaemons()
substitute input:'<<'!=''
create:definesubstitution(SplitCmd[1],SplitCmd[2:])
sub input:'<<'!='' create:definesubstitution(SplitCmd[1],SplitCmd[2:])
trace input:'<<'!='' create:toggletrace(SplitCmd[1])
set input:'<<'!='' input:'<<'!='' input:'<<'!='' +*
create:SetOption(SplitCmd[1],SplitCmd[2],'::SPACE::'.join(SplitCmd[3:]))
show options create:displayopts()
define daemon input:'<<'!='' create:createdaemon(SplitCmd[2])
def daemon input:'<<'!='' create:createdaemon(SplitCmd[2])
define schedule input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
input:'<<'!=''
create:scheduledaemon(SplitCmd[2],SplitCmd[3],SplitCmd[4],SplitCmd[5])
define sched input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
input:'<<'!=''
create:scheduledaemon(SplitCmd[2],SplitCmd[3],SplitCmd[4],SplitCmd[5])
def schedule input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
input:'<<'!=''
create:scheduledaemon(SplitCmd[2],SplitCmd[3],SplitCmd[4],SplitCmd[5])
def sched input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
input:'<<'!=''
create:scheduledaemon(SplitCmd[2],SplitCmd[3],SplitCmd[4],SplitCmd[5])
define task input:IsDaemon('<<') input:'<<'!='' +*
create:adddaemontask(SplitCmd[2],SplitCmd[3],SplitCmd[4:])
define collector input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
input:'<<'!='' input:'<<'!='' input:'<<'!='' input:'<<'!=''
create:adddaemontaskcollector(SplitCmd[2],SplitCmd[3],SplitCmd[4],SplitC
md[5],SplitCmd[6],SplitCmd[7],SplitCmd[8])
subscribe entity input:IsDaemon('<<') input:'<<'!=''
input:EntityManager.isEntity('<<')
create:adddaemontaskentity(SplitCmd[2],SplitCmd[3],SplitCmd[4])
subs entity input:IsDaemon('<<') input:'<<'!=''
input:EntityManager.isEntity('<<')
create:adddaemontaskentity(SplitCmd[2],SplitCmd[3],SplitCmd[4])
def task input:IsDaemon('<<') input:'<<'!='' +*
create:adddaemontask(SplitCmd[2],SplitCmd[3],SplitCmd[4:])
def collector input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
input:'<<'!='' input:'<<'!='' input:'<<'!='' input:'<<'!=''
create:adddaemontaskcollector(SplitCmd[2],SplitCmd[3],SplitCmd[4],SplitC
md[5],SplitCmd[6],SplitCmd[7],SplitCmd[8])
def alert input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
input:'<<'!='' input:'<<'!='' input:'<<'!=''
create:adddaemontaskcollectoralert(SplitCmd[2],SplitCmd[3],SplitCmd[4],S
plitCmd[5],SplitCmd[6],'::SPACE::'.join(SplitCmd[7:]))
define alert input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
input:'<<'!='' input:'<<'!='' input:'<<'!=''
create:adddaemontaskcollectoralert(SplitCmd[2],SplitCmd[3],SplitCmd[4],S
plitCmd[5],SplitCmd[6],'::SPACE::'.join(SplitCmd[7:]))
delete daemon input:IsDaemon('<<') create:removedaemon(SplitCmd[2])
del daemon input:IsDaemon('<<') create:removedaemon(SplitCmd[2])
delete task input:IsDaemon('<<') input:'<<'!=''
create:removedaemontask(SplitCmd[2],SplitCmd[3])
del task input:IsDaemon('<<') input:'<<'!=''
create:removedaemontask(SplitCmd[2],SplitCmd[3])
update task input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
create:updatedaemontask(SplitCmd[2],SplitCmd[3],SplitCmd[4:])
upd task input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
create:updatedaemontask(SplitCmd[2],SplitCmd[3],SplitCmd[4:])
delete collector input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
create:removedaemontaskcollector(SplitCmd[2],SplitCmd[3],SplitCmd[4])
del collector input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
create:removedaemontaskcollector(SplitCmd[2],SplitCmd[3],SplitCmd[4])
unsubscribe entity input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
create:removedaemontaskentity(SplitCmd[2],SplitCmd[3],SplitCmd[4])
unsub entity input:IsDaemon('<<') input:'<<'!='' input:'<<'!=''
create:removedaemontaskentity(SplitCmd[2],SplitCmd[3],SplitCmd[4])
activate daemon input:IsDaemon('<<') create:makedaemonlive(SplitCmd[2])
act daemon input:IsDaemon('<<') create:makedaemonlive(SplitCmd[2])
show active daemons create:showactivedaemons()
deactivate daemon input:IsDaemon('<<') create:killdaemon(SplitCmd[2])
deac daemon input:IsDaemon('<<') create:killdaemon(SplitCmd[2])
alerts create:showalertqueue()
handle input:'<<'!='' input:'<<'!=''
create:handlealertrange(int(SplitCmd[1]),int(SplitCmd[2]))
addline input:'<<'!='' +*
create:appendtoscript(SplitCmd[1],SplitCmd[2:])
insline input:'<<'!='' input:'<<'!='' +*
create:inserttoscript(SplitCmd[1],SplitCmd[2],SplitCmd[3:])
delline input:'<<'!='' input:'<<'!=''
create:delfromscript(SplitCmd[1],SplitCmd[2])
run input:isScript('<<') +* create:runscript(SplitCmd[1],SplitCmd[2:])
delete script input:'<<'!='' create:delscript(SplitCmd[2])
del script input:'<<'!='' create:delscript(SplitCmd[2])
show script input:'<<'!='' create:showscripts(SplitCmd[2])
show scripts create:showscripts('all')
message input:'<<'!='' +* create:message(SplitCmd[1:])
msg input:'<<'!='' +* create:message(SplitCmd[1:])
ENDDCOMMANDDEFS
Thankyou for your time pythoners, any suggestions / comments are much
appreciated.
Matt.
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