🌐 Mailman 3 February 2019 - Python-list - python.org

Re: Quirk difference between classes and functions
by Peter J. Holzer Feb. 28, 2019

Feb. 28, 2019

On 2019-02-27 12:34:37 -0500, Dennis Lee Bieber wrote: > On Tue, 26 Feb 2019 19:15:16 -0800 (PST), jfong(a)ms4.hinet.net declaimed the > following: > > >So, may I say that the Python compiler is a multi-pass one? > > No... that is implementation dependent... True, but > The common Python is a byte-code compiler pass (how many is undefined) > which then feeds a byte-code INTERPRETER. He's only talking about the byte-code compiler here, not the interpreter. > The compiler pass "sees" the local assignment, and creates a run-time > data structure for the function which "holds" the local data. Yup, but in def foo(): print(bar) bar = 1 the compiler sees the local assignment AFTER the print() call. So it can't generate code to access the local variable for the print call because it doesn't yet know that bar is a local variable. The obvious way around this is a two pass compiler: In the first pass you parse the whole function and convert it into an AST. While you do this you can also collect local variables. In the second pass you convert the AST to byte-code. I think it should be possible to do it in a single pass, although at the cost of generating less efficient code: For each variable access, produce code to check for a local variable first, then a global one. Collect information on local variables at the same time. When you are done, generate the code to set up the local variables and arrange for it to be executed before any other code in the function. hp -- _ | Peter J. Holzer | we build much bigger, better disasters now |_|_) | | because we have much more sophisticated | | | hjp(a)hjp.at | management tools. __/ | http://www.hjp.at/ | -- Ross Anderson <https://www.edge.org/>

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Re: Lifetime of a local reference
by Gregory Ewing Feb. 28, 2019

Feb. 28, 2019

Thomas Jollans wrote: > If the inspect module's stack frame inspection machinery is supported, > then any function call might access any local... (though I don't think a > compliant Python implementation necessarily has to support the inspect > module fully). You can be devious even without using the expect module: def fun(): f = open("lock.txt", "w") do_stuff(innocent_argument) do_stuff = exec innocent_argument = "f.write('foo')" -- Greg

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Quirk difference between classes and functions
by ast Feb. 28, 2019

Feb. 28, 2019

Hello I noticed a quirk difference between classes and functions >>> x=0 >>> >>> class Test: x = x+1 print(x) x = x+1 print(x) 1 2 >>> print(x) 0 Previous code doesn't generate any errors. x at the right of = in first "x = x+1" line is the global one (x=0), then x becomes local within a function, this is not allowed >>> x = 0 >>> >>> def f(): x = x+1 >>> f() UnboundLocalError: local variable 'x' referenced before assignment Since x is written inside the function, it is considered as a local variable and x in x+1 is undefined so this throw an exception Any comment ?

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Re: ANN: Creating GUI Applications with wxPython
by Dave Feb. 27, 2019

Feb. 27, 2019

On 2/27/19 11:38 AM, Rhodri James wrote: > On 27/02/2019 15:37, Dave wrote: >> * GUI must support all desktops with a native look and feel. Kivy >> fails this one. Will have mobile apps later in the year, so it would >> be nice if one GUI fits all, but am ok with 2 gui's if needed. > > This requirement will cause you endless pain, particularly when mobiles > enter the picture. I'm not convinced it's a completely good idea; a > sensible UI for a desktop probably won't be sensible for a phone and > vice versa > Agreed - that is why I'm open to two GUI kits. Dave

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ANN: Creating GUI Applications with wxPython
by Mike Driscoll Feb. 27, 2019

Feb. 27, 2019

Hi, I just thought I would let you all know that I am working on my 2nd wxPython book, "Creating GUI Applications with wxPython". This one will be about actually creating small runnable applications instead of just recipes like my Cookbook did. I hope to have 8-10 working applications included with the book. You can read more about it here if you are interested: https://www.blog.pythonlibrary.org/2019/01/14/creating-gui-applications-wit… Feel free to ask me questions about it too. Thanks, Mike

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Dictionary
by Himanshu Yadav Feb. 27, 2019

Feb. 27, 2019

fibs={0:0,1:1} def rfib(n): global fibs if not fibs.get(n): fibs[n]=rfib(n-2)+rfib(n-1) return fibs[n] Why it is gives error??

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Python 3 Boto Unable to parse pagination error
by Tim Dunphy Feb. 27, 2019

Feb. 27, 2019

Hi all, I'm trying to create a python 3 script that takes a list of AWS instance IDs. It then prints out some information about the instances and then terminates them. I am very new to python, so still working through some basic issues. This is the error I get when I run the script: python3 .\aws_ec2_termiante_instances.py Enter an instance ID separated by commas: i-0463897140af217f8,i-0634fc5fa453462fb enter code here Deleting Instance IDs: i-0463897140af217f8 i-0634fc5fa453462fb Traceback (most recent call last): File ".\aws_ec2_termiante_instances.py", line 37, in <module> NextToken='string' File "C:\Users\tdunphy\AppData\Local\Programs\Python\Python37-32\lib\site-packages\botocore\client.py", line 357, in _api_call return self._make_api_call(operation_name, kwargs) File "C:\Users\tdunphy\AppData\Local\Programs\Python\Python37-32\lib\site-packages\botocore\client.py", line 661, in _make_api_call raise error_class(parsed_response, operation_name) botocore.exceptions.ClientError: An error occurred (InvalidParameterValue) when calling the DescribeInstances operation: Unable to parse pagination token This is my script that produces the above output: from collections import defaultdict import boto3 # Connect to EC2 ec2 = boto3.client('ec2') instance_id_list = input("Enter an instance ID separated by commas: ") instance_ids_text = instance_id_list.split(",") print("Deleting Instance IDs:") for instance_id in instance_ids_text: print(instance_id) ec2info = defaultdict() for instance_id in instance_ids_text: instance = ec2.describe_instances( Filters=[ { 'Name': 'string', 'Values': [ 'string', ] }, ], InstanceIds=[ 'instance_id', ], MaxResults=123, NextToken='string' ) for tag in instance.tags: if 'Name'in tag['Key']: name = tag['Value'] # Add instance info to a dictionary ec2info[instance.id] = { 'Name': name, 'Instance ID': instance.id, 'Type': instance.instance_type, 'State': instance.state['Name'], 'Private IP': instance.private_ip_address, 'Public IP': instance.public_ip_address, 'Launch Time': instance.launch_time } attributes = ['Name', 'Instance ID', 'Type', 'State', 'Private IP', 'Public IP', 'Launch Time'] for instance_id, instance in ec2info.items(): for key in attributes: print("{0}: {1}".format(key, instance[key])) print("------") ec2.instances.filter(InstanceIds=instance.id).stop() ec2.instances.filter(InstanceIds=instance.id).terminate() To recap, what I would like to do is give the script a list of instance IDs, print out the list of instance IDs, then print some info about those instances. Then terminate them. How can I get past this error and produce that result? Thank you, Tim -- GPG me!! gpg --keyserver pool.sks-keyservers.net --recv-keys F186197B

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argparse namespace clashes
by Robin Becker Feb. 27, 2019

Feb. 27, 2019

After converting a previously working optparse I found that I should not be using 'args' as a destination as it seemed to break django 1.11 management command execution. I changed both the flag name '--args' to '--task-args' and the destination 'args' to 'task-args' and that seemed to fix things. Is there a recommendation anywhere for names and detinations to avoid? -- Robin Becker

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Re: Lifetime of a local reference
by Marko Rauhamaa Feb. 27, 2019

Feb. 27, 2019

Rhodri James <rhodri(a)kynesim.co.uk>: > On 27/02/2019 06:56, Marko Rauhamaa wrote: >> Then there's the question of a sufficient way to prevent premature >> garbage collection: >> >> def fun(): >> f = open("lock") >> flock.flock(f, fcntl.LOCK_EX) >> do_stuff() >> f.close() >> sys.exit(0) >> >> def fun(): >> f = open("lock") >> flock.flock(f, fcntl.LOCK_EX) >> do_stuff() >> f.close >> sys.exit(0) >> >> def fun(): >> f = open("lock") >> flock.flock(f, fcntl.LOCK_EX) >> do_stuff() >> f >> sys.exit(0) >> >> def fun(): >> f = open("lock") >> flock.flock(f, fcntl.LOCK_EX) >> do_stuff() >> sys.exit(0) > > I would go with: > > def fun(): > with open("lock") as f: > flock.flock(f, fcntl.LOCK_EX) > do_stuff() > sys.exit(0) > > The description of the with statement does explicitly say that the > context manager's __exit__() method won't be called until the suite > has been executed, so the reference to the open file must exist for at > least that long. Yeah, but the *true* answer, of course, is: def fun(): f = os.open("lock", os.O_RDONLY) flock.flock(f, fcntl.LOCK_EX) do_stuff() sys.exit(0) Collect that! ;-) Marko

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Multi meaning of label: Doc bug
by Rustom Mody Feb. 27, 2019

Feb. 27, 2019

Ref: This stackexchange post: https://unix.stackexchange.com/q/503241/323121 Context: Theres this guy who's really struggling with disk partitioning LVM etc concepts. That point is not directly relevant to this question. My answer on that post tries to clarify that 'label' can mean 3 things at least; and that just in the context of disks, partitions etc. Quite confusing!! My question: In his parted output he has Error: /dev/mapper/lubuntu--vg-home: unrecognised disk label In which sense is this 'label' used?? Is it the Open/Free-BSD sense? Or the partition label sense?

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