🌐 Mailman 3 June 2021 - Tutor - python.org

Scripting Calligra sheets with Python
by Jim Byrnes Jan. 31, 2022

Jan. 31, 2022

I am trying to script Calligra Sheets (formerly KSpread) with python. I have gotten some of the included example scripts to run so I know python scripting is running. I found the following snippet on their website: import KSpread sheet = KSpread.view().sheet() # swap text of B5 and C6 t1 = sheet.text("B5") t2 = sheet.text(6,3) sheet.setText("B5", t2) sheet.setText(6, 3, t1) # swap value of D7 and E8 v1 = sheet.value("D7") v2 = sheet.value(8,5) sheet.setValue("D7", v2) sheet.setValue(8, 5, v1) Error: 'str' object has no attribute 'text' File "file:///usr/share/kde4/apps/sheets/scripts/extensions/myswap.py", line 4, in <module> This error message appeared in a dialog box. I've taught myself some Python but I don't understand what is happening here. Shouldn't t1 be a sheet object? What would cause it to be a str instead? Thanks, Jim

5 8

Multiprocessing
by Pugliese, Francesco July 2, 2021

July 2, 2021

Dear all, I am Francesco and currently PhD at the University of Liverpool. I am trying to use the multiprocessing library in python to performance some structural analyses using Opensees (please see the attached file for reference). I am coding like this: if __name__=="__main__": p = Pool(8) p.map(fun, range(1,10001), chunksize = 1) p.terminate() p.join() After completing all analyses, the system does not close the pool but remains stuck (frozen) without doing anything. Could please help me out to understand where I am making mistakes? Thanks a lot. Kind Regards, Francesco - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Francesco, PUGLIESE, BEng, Meng, MRes, S.M.ASCE, MICE PhD Candidate in Risk Analysis and Earthquake Engineering Seismic Team School of Engineering Brodie Tower, 6th Floor, PostGraduate Research Office University of Liverpool, Liverpool, Uk

2 1

Readability: To use certain Python features or not?
by boB Stepp June 28, 2021

June 28, 2021

Questions inspired by an example from "Practical Programming, 3rd ed." by Gries, Campbell and Montojo. p. 221 example. Compare: [...] bird_to_observations = {} for line in observations_file: bird = line.strip() if bird in bird_to_observations: bird_to_observations[bird] = bird_to_obserations[bird] + 1 else: bird_to_observations[bird] = 1 [...] to [...] bird_to_observations = {} for line in observations_file: bird = line.strip() bird_to_observations[bird] = bird_to_observations.get(bird, 0) + 1 [...] The authors comment: "Using the get method makes the program shorter, but some programmers find it harder to understand at a glance..." To my mind *if* the reader is fully familiar with Python the second example is both shorter and more expressive. For the most maintainable code which of these is better? What assumptions about our code's future audience should we hold to best help our future readers of our code? Note that I am asking a different set of questions from another common topic: When to use Python constructs like list comprehensions, lambdas, etc., which can greatly shorten LOC, but easily become a sea of letters when one makes them too complex. TIA! boB Stepp

4 5

Re: [Tutor] Clarification questions about how Python uses references.
by boB Stepp June 28, 2021

June 28, 2021

On Fri, Jun 25, 2021 at 6:21 PM Dennis Lee Bieber <wlfraed(a)ix.netcom.com> wrote: > > On Fri, 25 Jun 2021 14:48:00 -0500, boB Stepp <robertvstepp(a)gmail.com> > declaimed the following: > > >The Wikipedia entry on MD5 states, "The MD5 message-digest algorithm > >is a widely used *hash function* [my emphasis] producing a 128-bit > >hash value." Looking up "hash function", the Wikipedia article on it > >states, "A hash function is any function that can be used to map data > >of arbitrary size to fixed-size values. The values returned by a hash > >function are called hash values, hash codes, digests, or simply > >hashes. The values are usually used to index a fixed-size table called > >a hash table." This seems to fit in perfectly well with what Cameron > >stated and my usage above seems to be correct. The "index" in this > >instance would be for the entire file that the MD5 value was computed > >for. This may be (ignorant?) quibbling on my part, but it seems that > >we spend much of our time on these mailing lists trying to be > >uber-precise in our language usage. I guess I am either falling into > >this trap or am engaging in a good thing? ~(:>)) > > > > But there is no /table/ being indexed by the MD5 hash! So how do you > locate the original file if given the MD5 hash? File systems that use > hashes use the file name, and don't hash the file contents (any edit of the > contents would invalidate the MD5 hash, and require regenerating the hash > value). The file name stays the same regardless of the edits to the file > itself, so its hash also stays the same.. I see your point better now; however, the hash function definition above does say, "...The values are *usually* [my emphasis] used to index..." I guess my (ignorant?) quibbling point is that MD5 is still by definition a hash function. But this nit is not worth picking. Everything you say sounds eminently practical and sane! Cheers! boB Stepp

4 3

Having issues with a simple port scanner using scapy
by Chris Verhalen June 28, 2021

June 28, 2021

I’m new to python andI have no idea where I went wrong to get this port scanner using Scapy to work properly. Any help is appreciated. import loggingfrom scapy.layers.inet import TCP, ICMP, IPlogging.getLogger("scapy.runtime").setLevel(logging.ERROR) # Disable the annoying No Route found warning !from scapy.all import *ip = "10.0.0.3"closed_ports = 0open_ports = []def is_up(ip): #""" Tests if host is up """ icmp = IP(dst=ip)/ICMP() resp = sr1(icmp, timeout=10) if resp == None: return False else: return Trueif __name__ == '__main__': conf.verb = 0 # Disable verbose in sr(), sr1() methods start_time = time.time() ports = range(1, 1024) if is_up(ip): print("Host %s is up, start scanning" % ip) for port in ports: src_port = RandShort() # Getting a random port as source port p = IP(dst=ip)/TCP(sport=src_port, dport=port, flags='S') # Forging SYN packet resp = sr1(p, timeout=2) # Sending packet if str(type(resp)) == "<type 'NoneType'>": closed += 1 elif resp.haslayer(TCP): if resp.getlayer(TCP).flags == 0x12: send_rst = sr(IP(dst=ip)/TCP(sport=src_port, dport=port, flags='AR'), timeout=1) openp.append(port) elif resp.getlayer(TCP).flags == 0x14: closed += 1 duration = time.time()-start_time print("%s Scan Completed in %fs" % (ip, duration)) if len(openp) != 0: for opp in openp: print("%d open" % pop) print("%d closed ports in %d total port scanned" % (closed, len(ports)) else: print("Host %s is Down" % ip) line 47 else: ^SyntaxError: invalid syntax Process finished with exit code 1

2 1

Count number of female names in dict
by Manprit Singh June 28, 2021

June 28, 2021

Dear sir, Consider a dict as given below : dic = {"Miss Preeti":30, "Master Paras": 31, "Master Jay": 30, "Miss Pooja": 32} The keys are names of students and values are marks obtained by them . Now if i have to count the number of female students (Names starting with Miss are female names ), can i do it in this way as given below ? sum(x.startswith("Miss") for x in dic.keys()) See the generator expression inside sum() function will return an iterator of True & False (True for females ), So i can say that passing this Generator expression inside sum() will give count of True that is 2 and is correct answer (There are only 2 female names). Is my way correct ? Regards Manprit Singh

2 1

Re: [Tutor] Clarification questions about how Python uses references.
by Cameron Simpson June 27, 2021

June 27, 2021

On 25Jun2021 19:20, Dennis Lee Bieber <wlfraed(a)ix.netcom.com> wrote: > But there is no /table/ being indexed by the MD5 hash! So how do you >locate the original file if given the MD5 hash? File systems that use >hashes use the file name, and don't hash the file contents (any edit of the >contents would invalidate the MD5 hash, and require regenerating the hash >value). The file name stays the same regardless of the edits to the file >itself, so its hash also stays the same.. The example of a file indexed by its MD5 hash I had in mind was a real world example of a client report request, and the corresponding output files. Receive the request, save it to disc for processing under a filename based on the MD5 checksum, save that filename in a work queue. The worker picks up the filename and makes the reports, likewise saving them for the client to collect. The MD5 here is used as an easy way to pick _unique_ filenames for the work request and its results. The request never changes content once received. Not the usage you had in mind, but valid nonetheless. A filename is effectively an index into a filesystem. A filename made directly from the MD5 of its contents in this case, as a free unique name in a shared work area. This is a similar use case to that for GUUIDs in other contexts. Cheers, Cameron Simpson <cs(a)cskk.id.au>

2 1

Re: [Tutor] What is the easiest way to ensure the current working directory is the same as the directory where the main program is saved?
by boB Stepp June 27, 2021

June 27, 2021

Please forgive the top posting in this instance. I want to ensure Dennis' response gets saved intact into the Tutor archives so I can easily find it later as his postings otherwise never show up unless someone responds to them. In summary of what you write below, Dennis, you are basically saying to me to store my data files in standard locations expected by each operating system that the program is installed into? Then this should be a no-brainer for the actual program to access its data and configuration files. But what about during a program's development phase? It is handy to have data files in the same project directory space as everything else. I have been doing some online searching and it appears that during an installation process that installers can copy data and configuration files to those standard locations that you are advocating. But again I know nothing about installing Python programs and the software that gets it done. I merely know how to use pip to install applications others have developed, not how to get my code ready for such a procedure. Anyway, thanks Dennis for your detailed response! boB Stepp On Sat, Jun 26, 2021 at 12:10 PM Dennis Lee Bieber <wlfraed(a)ix.netcom.com> wrote: > > On Fri, 25 Jun 2021 22:50:52 -0500, boB Stepp <robertvstepp(a)gmail.com> > declaimed the following: > > > ><Scratch head> But I *do* care about where my source code winds up, > >don't I? How else do I load data from its data folder if I don't know > >where I am in the user's file system? > > Most applications do not store live "data" in their installation > directory. On Windows, that is what each user's AppData directory is used > for (though many applications coming from Linux/UNIX background create > "dot" files in %userprofile% (in Linux, "dot" files are normally hidden) > > C:\Users\Wulfraed>echo %userprofile% > C:\Users\Wulfraed > > C:\Users\Wulfraed>dir %userprofile% > Volume in drive C is OS > Volume Serial Number is 4ACC-3CB4 > > Directory of C:\Users\Wulfraed > > 06/22/2021 03:05 PM <DIR> . > 06/22/2021 03:05 PM <DIR> .. > 12/05/2020 04:57 PM 6,514 .bash_history > 06/24/2021 06:28 PM 866 .flexprop.config > 07/29/2019 01:48 PM 166 .gitconfig > 09/13/2020 02:39 PM 2,277 .kdiff3rc > 05/31/2021 07:11 PM 1,367 .python_history > 05/07/2021 04:25 PM 2,596 .RData > 05/07/2021 04:25 PM 166 .Rhistory > > If the program requires default configuration to exist, it uses, > perhaps, __file__ to find the install directory, uses various os.path > methods to parse off the filename itself leaving the directory, and then > combines the directory with the known subpath/config-data -- and copies > that to the user specific location > > C:\Users\Wulfraed>echo %appdata% > C:\Users\Wulfraed\AppData\Roaming > > C:\Users\Wulfraed>dir %appdata% > Volume in drive C is OS > Volume Serial Number is 4ACC-3CB4 > > Directory of C:\Users\Wulfraed\AppData\Roaming > > 06/02/2021 02:51 PM <DIR> . > 06/02/2021 02:51 PM <DIR> .. > 12/03/2016 06:28 PM <DIR> .kde > 12/03/2016 06:28 PM <DIR> .mplab_ide > 12/03/2016 06:28 PM <DIR> .oit > 01/03/2017 01:54 AM <DIR> 5KPlayer > 12/03/2016 06:28 PM <DIR> Acronis > 10/10/2017 12:28 PM <DIR> Adobe > > > > >Maybe this is where my misunderstandings are occurring. To date, I > >have had no installation process. Any programs that I need to be > >elsewhere, I copy the program to its new living facilities, whether > >elsewhere on my PC, somewhere else on a network, or to another PC. > >Does an actual installation process make these issues go away? As a > >user of other people's programs that come with an installer one of the > >first choices the user usually must make is accept the default > >installation suggestion or choose a different location. I suppose > >this is where the needed information is fed into the program and > >stored for later use? > > The install location might be an entry in the Windows registry > (especially if the application has an uninstall feature). About the only > things done in an install directory (for Python) is to compile .py files > (modules) into .pyc; that often needs to use the local Python, and reduces > the distribution file size. > > An installer program may handle copying the default config files to the > user's directory, where the application expects to find them. > > > > >I thought I could put off figuring out how to install Python packages > >the "proper" way (if there is one) ... > > > > Are you talking packages you are writing? If so, the main feature is to > have them in a directory that Python searches during import. > > https://docs.python.org/3/tutorial/modules.html > """ > 6.1.2. The Module Search Path > > When a module named spam is imported, the interpreter first searches for a > built-in module with that name. If not found, it then searches for a file > named spam.py in a list of directories given by the variable sys.path. > sys.path is initialized from these locations: > > * The directory containing the input script (or the current directory > when no file is specified). > > * PYTHONPATH (a list of directory names, with the same syntax as the > shell variable PATH). > > * The installation-dependent default. > """ > > >------------------------ > >import os > > > >print("Testing!") > >print("Current working directory: ", os.getcwd()) > >print("Source code file: ", __file__) > >with open('test_text.txt') as f: > > print(f.read()) > >------------------------ > > > > with open(os.path.join(os.path.dirname(__file__), "test_text.txt")) as f: > > > > >How should I be handling these situations? > > > > Personally... by not putting /data/ in the application space. Arrange > for it to be in user-specific space... > > Windows: %userprofile%/.myapp/config or %appdata%/myapp/config > Linux: ~/.myapp/config > > Also consider the first bullet in the module search path quote... If > you arrange for your "data" to be a .py file, you should be able to just > > import config > > (may need to ensure you don't have conflicting names) > > > -- > Wulfraed Dennis Lee Bieber AF6VN > wlfraed(a)ix.netcom.com http://wlfraed.microdiversity.freeddns.org/ > > _______________________________________________ > Tutor maillist - Tutor(a)python.org > To unsubscribe or change subscription options: > https://mail.python.org/mailman/listinfo/tutor

2 1

What is the easiest way to ensure the current working directory is the same as the directory where the main program is saved?
by boB Stepp June 26, 2021

June 26, 2021

"Practical Programming -- An Introduction to Computer Science Using Python 3.6, 3rd ed." states on p. 177: "...When you run a Python program, the current working directory is the directory where that program is saved..." I have established that this is not true. The current working directory of the program depends on from what location the program is launched. Examples: Program: testing.py: -------------------------- import os print("Testing!") print("Current working directory: ", os.getcwd()) print("Source code file: ", __file__) Running program from different locations: ------------------------------------------------------- PS C:\Users\boB> Practical_Programming\testing.py Testing! Current working directory: C:\Users\boB Source code file: C:\Users\boB\Practical_Programming\testing.py PS C:\Users\boB> cd c:\ PS C:\> Users\boB\Practical_Programming\testing.py Testing! Current working directory: C:\ Source code file: C:\Users\boB\Practical_Programming\testing.py So this demonstrates that where you are when you launch a Python program determines its initial working directory. A handy thing for working in the interpreter when you want to import one of your own programs. Is there an _easy_ way to have a program start with its current working directory in the same directory where its source code resides no matter from where the program is launched? Or must I always use the __file__ attribute to determine where the source code resides and then change directories from there? How do people deal with their Python applications that in theory may be installed anywhere in a user's file system? There must be some standard way of dealing with this that I am too dense to uncover. TIA! boB Stepp

3 3

How to read the first so many Unicode characters from a file?
by boB Stepp June 26, 2021

June 26, 2021

Say I have a text file with a mixture of ASCII and non-ASCII characters (assumed to be UTF-8) and I wanted to read the first N characters from the file. The first thought that comes to mind is: with open(filename) as f: N_characters = f.read(N) But reading the docs says that this will read N bytes. My understanding is that some UTF-8 characters can be more than one byte. So it seems to me that this won't work in general. Does Python provide a way to accomplish this easily? Or is my understanding flawed? TIA! boB Stepp

2 4