[Tutor] Subprocess.Popen process seems to be outputting to stdout even though redirected ?
I have a simple script to tail a log file for an error string, it
works AOK but there is an unexpected side effect, when I run it in a
shell.
if I
echo "ERROR TEST" >> LOG
in a separate shell, I get the following from the script
ERROR TEST
GOT YA :)
ERROR TEST
So it looks like I am getting stdout from the tail -f, and two copies
of it ?, stdout should be piped to subprocess.stdout
tail = subprocess.Popen(['tail', '-f', LOG_FILE], shell=False,
stdout=subprocess.PIPE)
for out in iter(tail.stdout.readline, ''):
out_str = out.rstrip('\n')
if out_str.find('ERROR') != -1:
print 'GOT YA :)'
time.sleep(1)
Any ideas anyone ?
Cheers
Dave
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Re: [Tutor] Subprocess.Popen process seems to be outputting to stdout even though redirected ?
This list is amazing, I scratch my head, think and think then finally
post a question, maybe its the act of spelling it out, ps ax showed 2
x 'tail' processes, I am guessing zombies of previous attempts, killed
them, all works AOK now
On 10 June 2012 10:06, dave selby wrote:
> I have a simple script to tail a log file for an error string, it
> works AOK but there is an unexpected side effect, when I run it in a
> shell.
>
> if I
>
> echo "ERROR TEST" >> LOG
>
> in a separate shell, I get the following from the script
>
> ERROR TEST
> GOT YA :)
> ERROR TEST
>
> So it looks like I am getting stdout from the tail -f, and two copies
> of it ?, stdout should be piped to subprocess.stdout
>
> tail = subprocess.Popen(['tail', '-f', LOG_FILE], shell=False,
> stdout=subprocess.PIPE)
>
> for out in iter(tail.stdout.readline, ''):
>
> out_str = out.rstrip('\n')
>
> if out_str.find('ERROR') != -1:
> print 'GOT YA :)'
>
> time.sleep(1)
>
> Any ideas anyone ?
>
> Cheers
>
> Dave
>
> --
>
> Please avoid sending me Word or PowerPoint attachments.
> See http://www.gnu.org/philosophy/no-word-attachments.html
--
Please avoid sending me Word or PowerPoint attachments.
See http://www.gnu.org/philosophy/no-word-attachments.html
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[Tutor] properties beginner M Dawson book
Hi,
I am teaching myself Python with the book :Python Programming for the Absolute
Beginner, 3rd edition by M Dawson. It is an excellent book and I am enjoying
completing the challenges at the end of each chapter. There are,
unfortunately, no answers nor examples of good and bad code. Honestly I don’t
want to “cheat” but I have to teach Python to some young students in September,
using this book, and I want all the responses to any doubts they have ready
.
Here’s something specific:
chapter 8 challenge 2: “ Write a program that simulates a television by
creating it as an object. The user should be able to enter a channel number and
raise or lower the volume. Make sure that the channel number and volume level
stay within valid ranges.”
I have done a little programming in BlueJ Java before but I decided to try the
“Python style” as explained in the chapter, using properties rather than
variables and getters and setters .
My main question is: When using property and setter it seems I must use
“__name” or “__volume” (Python’s version of private variables). Is this true?
Here are parts of my code: - any comments about how bad / good this code is for
the level in the book (NOT advanced stuff please) would be greatly appreciated.
Thank you
class Television(object):
#Contstructor
def __init__(self, name, channel = 1, volume = 5):
print("A television has been made!")
#As I am using properties these assignments indirectly call the
#relevant property setter methods listed below
self.name = name
self.channel = channel
self.volume = volume
#Note: "self.__name = name" works but then no call is made to the
property setter method
@property
def name(self):
return self.__name
@name.setter
def name(self, newName):
if newName != "":
self.__name = newName
print("This TV is now called: ", self.__name)
else:
print("Sorry, empty string not allowed as a name.")
#If the setter was called in the middle of the program run
#that is it already has an attribute self.__name with a value
#So leave the namae as it was, unchanged.
try:
print("The name stays as: ", self.__name)
#This will generate an attribute error when called as part of
the __init__
#because self.name has not yet been created nor assigned.
#So catch this error and give self.__name a "default name"
except AttributeError:
self.__name = "Default"
print("The TV is now called: ", self.__name)
and
def main():
tv_name = input("What do you want to call your television? ")
tv = Television(tv_name)
choice = None
while choice != "0":
print \
("""
TV Maker
0 - Quit
1 - Television Details
2 - Set Channel
3 - Set Volume
4 - Chanage the name of the TV
""")
choice = input("Choice: ")
print()
# exit
if choice == "0":
print("Good-bye.")
# Print details of television
elif choice == "1":
print("Television details.")
print(tv)
# Change the channel
elif choice == "2":
amount = int(input("Enter 1 to 100 to choose a channel. "))
tv.channel = amount
# Change the volume
elif choice == "3":
amount = int(input("Enter 0 to 10 set the volume. "))
tv.volume = amount
elif choice == "4":
print("Choose a new name for your television but not nothing!")
tv.name = input("Enter a new name here: ")
# some unknown choice
else:
print("\nSorry, but", choice, "isn't a valid choice.")
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Re: [Tutor] properties beginner M Dawson book
Nicholas Harman wrote: I have done a little programming in BlueJ Java before but I decided to try the “Python style” as explained in the chapter, using properties rather than variables and getters and setters . My main question is: When using property and setter it seems I must use “__name” or “__volume” (Python’s version of private variables). Is this true? Certainly not. Python doesn't enforce any naming convention on you. You can use any name you like. But you *should* use something like "__name" or "__volume", simply because that will be more sensible than most other names. But if you choose to use something else, Python won't stop you. Note: you can also use just a single underscore, _name and _volume, to indicate that the attributes are private and should not be touched. -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] properties beginner M Dawson book
Nicholas Harman wrote:
class Television(object):
#Contstructor
Spelling error: Constructor.
Actually, technically __init__ is not the constructor. __init__ is the
initializer, as the object has already been created before __init__ is called.
__new__ is the constructor, although in this case it is unused.
def __init__(self, name, channel = 1, volume = 5):
Optional: it is the usual convention to declare default values without a
space, that is, __init__(self, name, channel=1, volume=5).
def main():
tv_name = input("What do you want to call your television? ")
Are you using Python 2, or Python 3?
If Python 3, this is fine. But in Python 2, you should use raw_input instead
of input.
tv = Television(tv_name)
choice = None
while choice != "0":
print \
("""
TV Maker
0 - Quit
1 - Television Details
2 - Set Channel
3 - Set Volume
4 - Chanage the name of the TV
""")
Spelling: Change, not Chanage.
The rest seems fine to me, assuming you are writing for beginners.
--
Steven
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