Re: try/except in a loop
Chris Kaynor wrote:
On Wed, May 2, 2012 at 12:51 PM, J. Mwebaze jmweb...@gmail.com wrote:
I have multiple objects, where any of them can serve my purpose.. However
some objects might not have some dependencies. I can not tell before hand if
the all the dependencies exsit. What i want to is begin processing from the
1st object, if no exception is raised, i am done.. if an exception is
raised, the next object is tried, etc Something like
objs = [... ]
try:
obj = objs[0]
obj.make()
except Exception, e:
try:
obj = objs[1]
obj.make()
except Exception, e:
try:
obj = objs[2]
obj.make()
except Exception, e:
continue
The problem is the length of the list of objs is variable... How can i do
this?
for obj in objs:
try:
obj.make()
except Exception:
continue
else:
break
else:
raise RuntimeError('No object worked')
For the record, an alternative solution without try block:
candidates = [obj for obj in objs if hasattr(obj, 'make') and
callable(obj.make)]
if candidates:
candidates[0].make()
JM
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Re: try/except in a loop
Jean-Michel Pichavant wrote:
Chris Kaynor wrote:
On Wed, May 2, 2012 at 12:51 PM, J. Mwebaze jmweb...@gmail.com wrote:
I have multiple objects, where any of them can serve my purpose..
However some objects might not have some dependencies. I can not tell
before hand if the all the dependencies exsit. What i want to is begin
processing from the 1st object, if no exception is raised, i am done..
if an exception is
raised, the next object is tried, etc Something like
objs = [... ]
try:
obj = objs[0]
obj.make()
except Exception, e:
try:
obj = objs[1]
obj.make()
except Exception, e:
try:
obj = objs[2]
obj.make()
except Exception, e:
continue
The problem is the length of the list of objs is variable... How can i
do this?
for obj in objs:
try:
obj.make()
except Exception:
continue
else:
break
else:
raise RuntimeError('No object worked')
For the record, an alternative solution without try block:
Hmm, it's not sufficient that the method exists, it should succeed, too.
class Obj:
def make(self):
raise Exception(I'm afraid I can't do that)
objs = [Obj()]
candidates = [obj for obj in objs if hasattr(obj, 'make') and
callable(obj.make)]
if candidates:
candidates[0].make()
It is often a matter of taste, but I tend to prefer EAFP over LBYL.
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Re: try/except in a loop
Peter Otten wrote:
Jean-Michel Pichavant wrote:
Chris Kaynor wrote:
On Wed, May 2, 2012 at 12:51 PM, J. Mwebaze jmweb...@gmail.com wrote:
I have multiple objects, where any of them can serve my purpose..
However some objects might not have some dependencies. I can not tell
before hand if the all the dependencies exsit. What i want to is begin
processing from the 1st object, if no exception is raised, i am done..
if an exception is
raised, the next object is tried, etc Something like
objs = [... ]
try:
obj = objs[0]
obj.make()
except Exception, e:
try:
obj = objs[1]
obj.make()
except Exception, e:
try:
obj = objs[2]
obj.make()
except Exception, e:
continue
The problem is the length of the list of objs is variable... How can i
do this?
for obj in objs:
try:
obj.make()
except Exception:
continue
else:
break
else:
raise RuntimeError('No object worked')
For the record, an alternative solution without try block:
Hmm, it's not sufficient that the method exists, it should succeed, too.
class Obj:
def make(self):
raise Exception(I'm afraid I can't do that)
objs = [Obj()]
candidates = [obj for obj in objs if hasattr(obj, 'make') and
callable(obj.make)]
if candidates:
candidates[0].make()
It is often a matter of taste, but I tend to prefer EAFP over LBYL.
Could be that the OP did its job by calling the make method if it
exists. If the method raises an exception, letting it through is a
viable option if you cannot handle the exception.
Additionaly, having a method not raising any exception is not a criteria
for success, for instance
def make(self):
return 42
will surely fail to do what the OP is expecting.
By the way on a unrelated topic, using try blocks to make the code
robust is never a good idea, I hope the OP is not try to do that.
JM
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try/except in a loop
I have multiple objects, where any of them can serve my purpose.. However some objects might not have some dependencies. I can not tell before hand if the all the dependencies exsit. What i want to is begin processing from the 1st object, if no exception is raised, i am done.. if an exception is raised, the next object is tried, etc Something like objs = [... ] try: obj = objs[0] obj.make() except Exception, e: try: obj = objs[1] obj.make() except Exception, e: try: obj = objs[2] obj.make() except Exception, e: continue The problem is the length of the list of objs is variable... How can i do this? -- *Mob UG: +256 (0) 70 1735800 | NL +31 (0) 6 852 841 38 | Gtalk: jmwebaze | skype: mwebazej | URL: www.astro.rug.nl/~jmwebaze /* Life runs on code */* -- http://mail.python.org/mailman/listinfo/python-list
Re: try/except in a loop
On Wed, May 2, 2012 at 12:51 PM, J. Mwebaze jmweb...@gmail.com wrote:
I have multiple objects, where any of them can serve my purpose.. However
some objects might not have some dependencies. I can not tell before hand if
the all the dependencies exsit. What i want to is begin processing from the
1st object, if no exception is raised, i am done.. if an exception is
raised, the next object is tried, etc Something like
objs = [... ]
try:
obj = objs[0]
obj.make()
except Exception, e:
try:
obj = objs[1]
obj.make()
except Exception, e:
try:
obj = objs[2]
obj.make()
except Exception, e:
continue
The problem is the length of the list of objs is variable... How can i do
this?
for obj in objs:
try:
obj.make()
except Exception:
continue
else:
break
else:
raise RuntimeError('No object worked')
--
Mob UG: +256 (0) 70 1735800 | NL +31 (0) 6 852 841 38 | Gtalk: jmwebaze |
skype: mwebazej | URL: www.astro.rug.nl/~jmwebaze
/* Life runs on code */
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Re: try/except in a loop
Why wouldn't a for loop work? If something works, you can break out, otherwise continue. working_obj = None for obj in iterable: try: obj.do_something() working_obj = obj break except: continue -- CPython 3.3.0a3 | Windows NT 6.1.7601.17790 -- http://mail.python.org/mailman/listinfo/python-list
Re: try/except in a loop
Forgot to add that all this is covered in the tutorial in the official docs: http://docs.python.org/tutorial/controlflow.html#for-statements -- CPython 3.3.0a3 | Windows NT 6.1.7601.17790 -- http://mail.python.org/mailman/listinfo/python-list
RE: try/except in a loop
I have multiple objects, where any of them can serve my purpose..
However
some objects might not have some dependencies. I can not tell before
hand if
the all the dependencies exsit. What i want to is begin processing from
the
1st object, if no exception is raised, i am done.. if an exception is
raised, the next object is tried, etc Something like
objs = [... ]
try:
obj = objs[0]
obj.make()
except Exception, e:
try:
obj = objs[1]
obj.make()
except Exception, e:
try:
obj = objs[2]
obj.make()
except Exception, e:
continue
The problem is the length of the list of objs is variable... How can i
do
this?
for obj in objs:
try:
obj.make()
except Exception:
continue
else:
break
else:
raise RuntimeError('No object worked')
I think you misunderstand the else clauses.
for obj in [ 1,2,3,4 ]:
... try:
... print obj
... except Exception:
... print 'EXCEPTION'
... else:
... print 'NO EXCEPTION'
... else:
... print 'NO OBJECTS'
...
1
NO EXCEPTION
2
NO EXCEPTION
3
NO EXCEPTION
4
NO EXCEPTION
NO OBJECTS
Ramit
Ramit Prasad | JPMorgan Chase Investment Bank | Currencies Technology
712 Main Street | Houston, TX 77002
work phone: 713 - 216 - 5423
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This email is confidential and subject to important disclaimers and
conditions including on offers for the purchase or sale of
securities, accuracy and completeness of information, viruses,
confidentiality, legal privilege, and legal entity disclaimers,
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Re: try/except in a loop
On Wed, May 2, 2012 at 1:12 PM, Prasad, Ramit ramit.pra...@jpmorgan.com wrote:
I have multiple objects, where any of them can serve my purpose..
However
some objects might not have some dependencies. I can not tell before
hand if
the all the dependencies exsit. What i want to is begin processing from
the
1st object, if no exception is raised, i am done.. if an exception is
raised, the next object is tried, etc Something like
objs = [... ]
try:
obj = objs[0]
obj.make()
except Exception, e:
try:
obj = objs[1]
obj.make()
except Exception, e:
try:
obj = objs[2]
obj.make()
except Exception, e:
continue
The problem is the length of the list of objs is variable... How can i
do
this?
for obj in objs:
try:
obj.make()
except Exception:
continue
else:
break
else:
raise RuntimeError('No object worked')
I think you misunderstand the else clauses.
for obj in [ 1,2,3,4 ]:
... try:
... print obj
... except Exception:
... print 'EXCEPTION'
... else:
... print 'NO EXCEPTION'
... else:
... print 'NO OBJECTS'
...
1
NO EXCEPTION
2
NO EXCEPTION
3
NO EXCEPTION
4
NO EXCEPTION
NO OBJECTS
You left out the break in the try clause's else that I had. That break
statement causes the for loop to exit early if there is no exception,
and thus the for loop's else clause does not run:
for obj in [ 1,2,3,4 ]:
... try:
... print obj
... except Exception:
... print 'EXCEPTION'
... else:
... print 'NO EXCEPTION'
... break
... else:
... print 'NO OBJECTS'
...
1
NO EXCEPTION
Ramit
Ramit Prasad | JPMorgan Chase Investment Bank | Currencies Technology
712 Main Street | Houston, TX 77002
work phone: 713 - 216 - 5423
--
This email is confidential and subject to important disclaimers and
conditions including on offers for the purchase or sale of
securities, accuracy and completeness of information, viruses,
confidentiality, legal privilege, and legal entity disclaimers,
available at http://www.jpmorgan.com/pages/disclosures/email.
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RE: try/except in a loop
for obj in objs:
try:
obj.make()
except Exception:
continue
else:
break
else:
raise RuntimeError('No object worked')
I think you misunderstand the else clauses.
for obj in [ 1,2,3,4 ]:
... try:
... print obj
... except Exception:
... print 'EXCEPTION'
... else:
... print 'NO EXCEPTION'
... else:
... print 'NO OBJECTS'
...
1
NO EXCEPTION
2
NO EXCEPTION
3
NO EXCEPTION
4
NO EXCEPTION
NO OBJECTS
You left out the break in the try clause's else that I had. That break
statement causes the for loop to exit early if there is no exception,
and thus the for loop's else clause does not run:
for obj in [ 1,2,3,4 ]:
... try:
... print obj
... except Exception:
... print 'EXCEPTION'
... else:
... print 'NO EXCEPTION'
... break
... else:
... print 'NO OBJECTS'
...
1
NO EXCEPTION
Whoops, you are right. My apologies Chris!
Ramit
Ramit Prasad | JPMorgan Chase Investment Bank | Currencies Technology
712 Main Street | Houston, TX 77002
work phone: 713 - 216 - 5423
--
This email is confidential and subject to important disclaimers and
conditions including on offers for the purchase or sale of
securities, accuracy and completeness of information, viruses,
confidentiality, legal privilege, and legal entity disclaimers,
available at http://www.jpmorgan.com/pages/disclosures/email.
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