Hi all !
I'm trying to capture stderr of an external module I use in my python
program. I'm doing this
by setting up a class in my module overwriting the stderr file object
method write.
The external module outputs to stderr this way:
from sys import std err
.....
print >stderr, "Some text"
While in my module I use
import sys
..... sys.stderr ... sys.stdout
Well, as long as I do not change in the external module those from/
import statements to just
import sys
.....
print >sys.stderr, "Some text"
I'm not able to capture its stderr and of course I would like not to
do this kind of change.
I've always been convinced of the equivalence of the two ways of using
the import statement
but it's clear I'm wrong :-(
Please, someone can tell me what's going on ?
Thanks in advance ! 10 1572
nisp schrieb:
Hi all !
I'm trying to capture stderr of an external module I use in my python
program. I'm doing this
by setting up a class in my module overwriting the stderr file object
method write.
The external module outputs to stderr this way:
from sys import std err
....
print >stderr, "Some text"
While in my module I use
import sys
..... sys.stderr ... sys.stdout
Well, as long as I do not change in the external module those from/
import statements to just
import sys
....
print >sys.stderr, "Some text"
I'm not able to capture its stderr and of course I would like not to
do this kind of change.
I've always been convinced of the equivalence of the two ways of using
the import statement
but it's clear I'm wrong :-(
Please, someone can tell me what's going on ?
http://effbot.org/zone/import-confusion.htm
Diez
nisp <emanuele.nesp...@gmail.comwrote:
I've always been convinced of the equivalence of the two ways of using
the import statement but it's clear I'm wrong :-(
Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52)
[GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>from sys import stderr import sys sys.stderr is stderr
True
Behaviourly, I'm finding no difference between the two either.
Could you cut & paste a minimal example that isn't producing the
correct behaviour, and perhaps mention what type of OS you're using?
alex23 schrieb:
nisp <emanuele.nesp...@gmail.comwrote:
>I've always been convinced of the equivalence of the two ways of using the import statement but it's clear I'm wrong :-(
Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52)
[GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>from sys import stderr import sys sys.stderr is stderr
True
Behaviourly, I'm finding no difference between the two either.
Could you cut & paste a minimal example that isn't producing the
correct behaviour, and perhaps mention what type of OS you're using?
You did not read this part of the post:
"""
I'm not able to capture its stderr and of course I would like not to
do this kind of change.
"""
He tries to set sys.stderr to a new stream and capture the print
statements, but fails to do so because he created a local alias.
Diez
nisp wrote:
Hi all !
I'm trying to capture stderr of an external module I use in my python
program. I'm doing this
by setting up a class in my module overwriting the stderr file object
method write.
The external module outputs to stderr this way:
from sys import std err
....
print >stderr, "Some text"
While in my module I use
import sys
..... sys.stderr ... sys.stdout
Well, as long as I do not change in the external module those from/
import statements to just
import sys
....
print >sys.stderr, "Some text"
I'm not able to capture its stderr and of course I would like not to
do this kind of change.
I've always been convinced of the equivalence of the two ways of using
the import statement
but it's clear I'm wrong :-(
Please, someone can tell me what's going on ?
Thanks in advance !
A practical approach to complement Diez' link to the explanation:
Instead of modifying the external module you can either redirect stderr
before you import the external module
import sys
sys.stderr = whatever
import external
or monkey-patch:
import sys
import external
sys.stderr = external.sterr = whatever
Peter
On Aug 27, 9:56 am, Peter Otten <__pete...@web.dewrote:
nisp wrote:
Hi all !
I'm trying to capture stderr of an external module I use in my python
program. I'm doing this
by setting up a class in my module overwriting the stderr file object
method write.
The external module outputs to stderr this way:
from sys import std err
....
print >stderr, "Some text"
While in my module I use
import sys
..... sys.stderr ... sys.stdout
Well, as long as I do not change in the external module those from/
import statements to just
import sys
....
print >sys.stderr, "Some text"
I'm not able to capture its stderr and of course I would like not to
do this kind of change.
I've always been convinced of the equivalence of the two ways of using
the import statement
but it's clear I'm wrong :-(
Please, someone can tell me what's going on ?
Thanks in advance !
A practical approach to complement Diez' link to the explanation:
Instead of modifying the external module you can either redirect stderr
before you import the external module
import sys
sys.stderr = whatever
import external
or monkey-patch:
import sys
import external
sys.stderr = external.sterr = whatever
Peter
Hi all !
Thanks first of all ! I read the interesting Diez's link but something
still remains to me unclear, on the other hand it's clear the my
problem is concentrated there and on symbols.
Here is what I'm trying to do
HelloWorld.py: this is a real simplification of my external module
though still reflecting its structure (commented out is the version
that, let's say, works)
from sys import stderr
#import sys
class Cheers:
def __init__(self):
self.cheersMsg = 'Hello World !!'
print "Cheers stderr %s" % stderr
#print "Cheers stderr %s" % sys.stderr
def _putCheers(self):
print>>stderr, 'Here is my msg:', self.cheersMsg
print>>stderr, 'This is a nice day today !!'
#print>>sys.stderr, 'Here is my msg:', self.cheersMsg
#print>>sys.stderr, 'This is a nice day today !!'
def doSomeStuff(self):
self._putCheers()
And below there is the module that uses the above one (mymodule.py):
#!/usr/bin/python
import sys
from HelloWorld import *
class StderrCatcher:
def __init__(self):
self.data = ''
def write(self,stuff):
self.data = self.data + "\t" + stuff
def main():
print "mymodule stderr: %s" % sys.stderr
sys.stderr = stderr = StderrCatcher()
m = Cheers()
m.doSomeStuff()
print "stderr: \n%s" % sys.stderr.data
if __name__ == '__main__':
main()
Below there is the output when it doesn't work:
mymodule stderr: <open file '<stderr>', mode 'w' at 0xb7d160b0>
Cheers stderr <open file '<stderr>', mode 'w' at 0xb7d160b0>
Here is my msg: Hello World !!
This is a nice day today !!
stderr:
And here when it works:
mymodule stderr: <open file '<stderr>', mode 'w' at 0xb7dc40b0>
Cheers stderr <__main__.StderrCatcher instance at 0xb7d8bd4c>
stderr:
Here is my msg: Hello World !!
This is a nice day today !!
Thanks again!
PS Sorry for having probably replied to somone of you directly :-(
nisp wrote:
On Aug 27, 9:56 am, Peter Otten <__pete...@web.dewrote:
>nisp wrote:
Hi all !
I'm trying to capture stderr of an external module I use in my python
program. I'm doing this
by setting up a class in my module overwriting the stderr file object
method write.
The external module outputs to stderr this way:
from sys import std err
....
print >stderr, "Some text"
While in my module I use
import sys
..... sys.stderr ... sys.stdout
Well, as long as I do not change in the external module those from/
import statements to just
import sys
....
print >sys.stderr, "Some text"
I'm not able to capture its stderr and of course I would like not to
do this kind of change.
I've always been convinced of the equivalence of the two ways of using
the import statement
but it's clear I'm wrong :-(
Please, someone can tell me what's going on ?
Thanks in advance !
A practical approach to complement Diez' link to the explanation:
Instead of modifying the external module you can either redirect stderr before you import the external module
import sys sys.stderr = whatever import external
or monkey-patch:
import sys import external
sys.stderr = external.sterr = whatever
Peter
Hi all !
Thanks first of all ! I read the interesting Diez's link but something
still remains to me unclear, on the other hand it's clear the my
problem is concentrated there and on symbols.
Here is what I'm trying to do
HelloWorld.py: this is a real simplification of my external module
though still reflecting its structure (commented out is the version
that, let's say, works)
from sys import stderr
This is your problem. You create a HelloWorld.stderr-alias to the object
bound to sys.stderr. Rebinding the latter won't affect the former. That is
precisely what the link I gave you explains.
The short answer to the whole issue is: dont' use the from-import syntax
until you really know what you are doing. Or not at all.
Diez
On Aug 27, 2:43 pm, "Diez B. Roggisch" <de...@nospam.web.dewrote:
nisp wrote:
On Aug 27, 9:56 am, Peter Otten <__pete...@web.dewrote:
nisp wrote:
Hi all !
I'm trying to capture stderr of an external module I use in my python
program. I'm doing this
by setting up a class in my module overwriting the stderr file object
method write.
The external module outputs to stderr this way:
from sys import std err
....
print >stderr, "Some text"
While in my module I use
import sys
..... sys.stderr ... sys.stdout
Well, as long as I do not change in the external module those from/
import statements to just
import sys
....
print >sys.stderr, "Some text"
I'm not able to capture its stderr and of course I would like not to
do this kind of change.
I've always been convinced of the equivalence of the two ways of using
the import statement
but it's clear I'm wrong :-(
Please, someone can tell me what's going on ?
Thanks in advance !
A practical approach to complement Diez' link to the explanation:
Instead of modifying the external module you can either redirect stderr
before you import the external module
import sys
sys.stderr = whatever
import external
or monkey-patch:
import sys
import external
sys.stderr = external.sterr = whatever
Peter
Hi all !
Thanks first of all ! I read the interesting Diez's link but something
still remains to me unclear, on the other hand it's clear the my
problem is concentrated there and on symbols.
Here is what I'm trying to do
HelloWorld.py: this is a real simplification of my external module
though still reflecting its structure (commented out is the version
that, let's say, works)
from sys import stderr
This is your problem. You create a HelloWorld.stderr-alias to the object
bound to sys.stderr. Rebinding the latter won't affect the former. That is
precisely what the link I gave you explains.
The short answer to the whole issue is: dont' use the from-import syntax
until you really know what you are doing. Or not at all.
Diez
Hi Diez! I well understand the problem now, the fact is that
unfortunately the external module is not mine and i doubt i can change
it :-( Anyway as far as i'm concerned i've learned the lesson ! Thanks
again and greetings,
Nisp
nisp wrote:
Thanks first of all ! I read the interesting Diez's link but something
still remains to me unclear, on the other hand it's clear the my
problem is concentrated there and on symbols.
Read it again. If you have two modules
module1.py
from sys import stderr
module2.py
from module1 import stderr
you get three names 'stderr' in three different namespaces, and each name
may bind a different object.
Here is what I'm trying to do
HelloWorld.py: this is a real simplification of my external module
though still reflecting its structure (commented out is the version
that, let's say, works)
from sys import stderr
#import sys
class Cheers:
Â*Â*Â*Â*Â*Â*Â*Â*def __init__(self):
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*self.cheersMsg = 'Hello World !!'
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*print "Cheers stderr %s" % stderr
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*#print "Cheers stderr %s" % sys.stderr
Â*Â*Â*Â*Â*Â*Â*Â*def _putCheers(self):
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*print>>stderr, 'Here is my msg:', self.cheersMsg
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*print>>stderr, 'This is a nice day today !!'
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*#print>>sys.stderr , 'Here is my msg:', self.cheersMsg
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*#print>>sys.stderr , 'This is a nice day today !!'
Â*Â*Â*Â*Â*Â*Â*Â*def doSomeStuff(self):
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*self._putCheers()
And below there is the module that uses the above one (mymodule.py):
#!/usr/bin/python
import sys
This imports HelloWorld.stderr:
from HelloWorld import *
You now have a global variable 'stderr' in module __main__, initialized to
the same value as HelloWorld.stderr.
class StderrCatcher:
Â*Â*Â*Â*Â*Â*Â*Â*def __init__(self):
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*self.data = ''
Â*Â*Â*Â*Â*Â*Â*Â*def write(self,stuff):
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*self.data = self.data + "\t" + stuff
def main():
Â*Â*Â*Â*Â*Â*Â*Â*print "mymodule stderr: %s" % sys.stderr
This rebinds sys.stderr and a local 'stderr' in main()
Â*Â*Â*Â*Â*Â*Â*Â*sys.stderr = stderr = StderrCatcher()
but both HelloWorld.stderr and __main__.stderr are unaffected. What you need
is
import HelloWorld
sys.stderr = HelloWorld.stderr = StderrCatcher()
Â*Â*Â*Â*Â*Â*Â*Â*m = Cheers()
Â*Â*Â*Â*Â*Â*Â*Â*m.doSomeStuff()
Â*Â*Â*Â*Â*Â*Â*Â*print "stderr: \n%s" % sys.stderr.data
if __name__ == '__main__':
Â* Â* main()
Below there is the output when it doesn't work:
mymodule stderr: <open file '<stderr>', mode 'w' at 0xb7d160b0>
Cheers stderr <open file '<stderr>', mode 'w' at 0xb7d160b0>
Here is my msg: Hello World !!
This is a nice day today !!
stderr:
And here when it works:
mymodule stderr: <open file '<stderr>', mode 'w' at 0xb7dc40b0>
Cheers stderr <__main__.StderrCatcher instance at 0xb7d8bd4c>
stderr:
Â* Â* Â* Â* Here is my msg: Â* Â* Â* Â* Hello World !!
Â* Â* Â* Â* This is a nice day today !!
Thanks again!
PS Sorry for having probably replied to somone of you directly :-(
On Aug 27, 5:42*pm, "Diez B. Roggisch" <de...@nospam.web.dewrote:
alex23 schrieb:
nisp <emanuele.nesp...@gmail.comwrote:
I've always been convinced of the equivalence of the two ways of using
the import statement but it's clear I'm wrong :-(
Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52)
[GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>from sys import stderr import sys sys.stderr is stderr
True
Behaviourly, I'm finding no difference between the two either.
Could you cut & paste a minimal example that isn't producing the
correct behaviour, and perhaps mention what type of OS you're using?
You did not read this part of the post:
"""
I'm not able to capture its stderr and of course I would like not to
do this kind of change.
"""
He tries to set sys.stderr to a new stream and capture the print
statements, but fails to do so because he created a local alias.
No, I read it, I just totally didn't parse it that way :)
Sorry for the confusion, nisp.
On Aug 27, 3:35 pm, Peter Otten <__pete...@web.dewrote:
nisp wrote:
Thanks first of all ! I read the interesting Diez's link but something
still remains to me unclear, on the other hand it's clear the my
problem is concentrated there and on symbols.
Read it again. If you have two modules
module1.py
from sys import stderr
module2.py
from module1 import stderr
you get three names 'stderr' in three different namespaces, and each name
may bind a different object.
Here is what I'm trying to do
HelloWorld.py: this is a real simplification of my external module
though still reflecting its structure (commented out is the version
that, let's say, works)
from sys import stderr
#import sys
class Cheers:
def __init__(self):
self.cheersMsg = 'Hello World !!'
print "Cheers stderr %s" % stderr
#print "Cheers stderr %s" % sys.stderr
def _putCheers(self):
print>>stderr, 'Here is my msg:', self.cheersMsg
print>>stderr, 'This is a nice day today !!'
#print>>sys.stderr, 'Here is my msg:', self.cheersMsg
#print>>sys.stderr, 'This is a nice day today !!'
def doSomeStuff(self):
self._putCheers()
And below there is the module that uses the above one (mymodule.py):
#!/usr/bin/python
import sys
This imports HelloWorld.stderr:
from HelloWorld import *
You now have a global variable 'stderr' in module __main__, initialized to
the same value as HelloWorld.stderr.
class StderrCatcher:
def __init__(self):
self.data = ''
def write(self,stuff):
self.data = self.data + "\t" + stuff
def main():
print "mymodule stderr: %s" % sys.stderr
This rebinds sys.stderr and a local 'stderr' in main()
sys.stderr = stderr = StderrCatcher()
but both HelloWorld.stderr and __main__.stderr are unaffected. What you need
is
import HelloWorld
sys.stderr = HelloWorld.stderr = StderrCatcher()
m = Cheers()
m.doSomeStuff()
print "stderr: \n%s" % sys.stderr.data
if __name__ == '__main__':
main()
Below there is the output when it doesn't work:
mymodule stderr: <open file '<stderr>', mode 'w' at 0xb7d160b0>
Cheers stderr <open file '<stderr>', mode 'w' at 0xb7d160b0>
Here is my msg: Hello World !!
This is a nice day today !!
stderr:
And here when it works:
mymodule stderr: <open file '<stderr>', mode 'w' at 0xb7dc40b0>
Cheers stderr <__main__.StderrCatcher instance at 0xb7d8bd4c>
stderr:
Here is my msg: Hello World !!
This is a nice day today !!
Thanks again!
PS Sorry for having probably replied to somone of you directly :-(
Hi Peter!
Definitely you are right ! May be this time I understood completely
the topic (or may be not ?... gosh !) ... I didn't considered well the
"from HelloWolrd import *" in mymodule.py.
Now my module is:
import sys
import HelloWorld
class StderrCatcher:
def __init__(self):
self.data = ''
def write(self,stuff):
self.data = self.data + "\t" + stuff
def main():
print "mymodule stderr: %s" % sys.stderr
mystderr = sys.stderr = HelloWorld.stderr = StderrCatcher()
m = HelloWorld.Cheers()
m.doSomeStuff()
print >>sys.stderr, "mymodule prints something"
print "stderr: \n%s" % mystderr.data
if __name__ == '__main__':
main()
and its output is:
mymodule stderr: <open file '<stderr>', mode 'w' at 0xb7d2d0b0>
Cheers stderr <__main__.StderrCatcher instance at 0xb7cf4e4c>
stderr:
Here is my msg: Hello World !!
This is a nice day today !!
mymodule prints something
now it works perfectly !
Great ! Thanks to all of you !
Nisp This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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