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

Most elegant way to do something N times
by Batuhan Taskaya Dec. 24, 2019

Dec. 24, 2019

I encounter with cases like doing a function 6 time with no argument, or same arguments over and over or doing some structral thing N times and I dont know how elegant I can express that to the code. I dont know why but I dont like this for _ in range(n): do() thing. Any suggestions?

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Lists And Extra Commas at end
by Avi Gross Dec. 24, 2019

Dec. 24, 2019

Marco, Python is used by some in an interactive mode but also in more of a batch mode such as on a server. The former can possibly see a SyntaxWarning. Do you want that as a default or something you set when you start the Python Interpreter or perhaps a command within it? I note a brief search to see about Warnings in Jupyter keeps talking about how to turn warnings off! My point is that warnings about what is not a real problem tend to make people ignore all warnings. Let me switch gears to the terminal comma situation. Unlike many languages, Python decided a dangling comma is perfectly allowable in many situations, perhaps all. >>> a=[1,2,3,] >>> a [1, 2, 3] The above does not work for an empty comma at the beginning or middle or a double comma at the end. It is clear why they allowed this as it makes some things easier like building up a list in a loop and not needing to figure out the special case when you are done and suppressing the last comma. Since a function argument list is just a list in Python, the following works fine: def testink(a,b,): pass And, of course, you can use the same dangling comma in making a tuple, dictionary or set and who knows where else. So, is that a feature you want warnings about? After all, a dangling comma may simply mean you left something out and meant to add later? As I see it, languages have tradeoffs and nobody will be completely satisfied so you choose and hope. But, warnings you can turn on an off do indeed make sense. But at what level? If the main interpreter has to do all kinds of testing even for a VALID use of the language so it can warn, that is extra overhead each time it is run. I would prefer something less intrusive. Some languages have a way of saying "use strict" (such as JavaScript or Perl) or a "use warnings" that tells to interpreter to warn about things. Since Python did not go this route, with perhaps a tad of that regarding the __future__ setting, I figured a good place to do this is in a Lint type of program that can be set to look for things that are not so much errors as places to check to make sure things are OK. You would not run that every time, just when the code has been changed. And, if you look for a list of places people make mistakes that are often maddening to trace, there are so many. Would you like a warning that multiple NAMES are almost the same except for capitalization or that you have long_variable_1_of_2 as well as long_variable_2_of_2 which only differ by a tad deep in the middle? At some point, you have to take the training wheels off. Not clear what that point is, sometimes, so I try to only drive vehicles with 4 or six tires, LOL! -----Original Message----- From: forwardedby(a)e4ward.com <forwardedby(a)e4ward.com> On Behalf Of Marco Sulla Sent: Tuesday, December 24, 2019 4:03 PM To: Avi Gross <avigross(a)verizon.net> Cc: Python-list.python.org-mail.python.org.marco.sulla.e4ward.com(a)jq38efsu937.reply.e4ward.com Subject: Re: Lists And Missing Commas On Tue, 24 Dec 2019 at 19:05, Avi Gross via Python-list <python-list(a)python.org> wrote: > There are some lint programs that check your code and supply warnings > and I see some languages have the option to generate warnings when the > two strings are on the same line. I wonder if a Python lint does that. > It may at least warn of this usage in time to check the code and put back the comma. IMHO it's not something that should be delegated to linter, but to the AST compiler itself. A SyntaxWarning should be displayed. One time I spent HOURS because I forgot one single comma in a list of strings. After that, my life is changed. I'm no more an ingenuous, little boy, that trusted the stacktrace.

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More efficient/elegant branching
by Musbur Dec. 24, 2019

Dec. 24, 2019

Hello, I have a function with a long if/elif chain that sets a couple of variables according to a bunch of test expressions, similar to function branch1() below. I never liked that approach much because it is clumsy and repetetive, and pylint thinks so as well. I've come up with two alternatives which I believe are less efficient due to the reasons given in the respective docstrings. Does anybody have a better idea? def branch1(a, b, z): """Inelegant, unwieldy, and pylint complains about too many branches""" if a > 4 and b == 0: result = "first" elif len(z) < 2: result = "second" elif b + a == 10: result = "third" return result def branch2(a, b, z): """Elegant but inefficient because all expressions are pre-computed althogh the first one is most likely to hit""" decision = [ (a > 4 and b == 0, "first"), (len(z) < 2, "second"), (b + a == 10, "third")] for (test, result) in decision: if test: return result def branch3(a, b, z): """Elegant but inefficient because expressions need to be parsed each time""" decision = [ ("a > 4 and b == 0", "first"), ("len(z) < 2", "second"), ("b + a == 10", "third")] for (test, result) in decision: if eval(test): return result (env) [dh@deham01in015:~/python/rscl_fdc/devel]$

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Re: Lists And Missing Commas
by Tim Daneliuk Dec. 24, 2019

Dec. 24, 2019

On 12/23/19 8:35 PM, Chris Angelico wrote: > On Tue, Dec 24, 2019 at 12:56 PM DL Neil via Python-list > <python-list(a)python.org> wrote: >> However, your point involves the fact that whereas: >> >> 1 + 2 # 3 is *clearly* addition, and >> "a" + "b" # "ab" is *clearly* concatenation >> >> "a" "b" # also evaluates to "ab" >> >> and is thus, concatenation without any explicit infix operator! Just one >> cotton-picking minute - what's going on here? > > 1_2 # Clearly concatenation. Right? > 0_0 # Clearly an emoticon > > Just another cotton-picking minute...... > > ChrisA > You are excused and required to do 30 days penance writing .NET.

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Re: [ANN] Retrospective of Python compilation efforts
by Guido van Rossum Dec. 24, 2019

Dec. 24, 2019

Nice work. On Tue, Dec 24, 2019 at 2:59 AM Paul Sokolovsky <pmiscml(a)gmail.com> wrote: > Hello, > > Over the years, the Python community produced many compiler projects for > the language, second to probably only C and LISP. Majority are of > course of research and proof of concept quality, but there're a number > of quite advanced projects. > > For some time, I was trying to compile a retrospective of these > efforts, formatted as a github "awesome" list: > > https://github.com/pfalcon/awesome-python-compilers > > > Happy holidays, > Paul > -- > Python-announce-list mailing list -- python-announce-list(a)python.org > To unsubscribe send an email to python-announce-list-leave(a)python.org > https://mail.python.org/mailman3/lists/python-announce-list.python.org/ > > Support the Python Software Foundation: > http://www.python.org/psf/donations/ > -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-…>

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Re: Lists And Missing Commas
by Tim Daneliuk Dec. 24, 2019

Dec. 24, 2019

On 12/24/19 6:37 AM, Stefan Ram wrote: > And you all are aware that this kind of string concatenation > happens in C and C++, too, aren't you? > > main.c > > #include <stdio.h> > int main( void ){ puts( "a" "b" ); } > > transcript > > ab Noting that it has been a long time since I looked at the C specification ... Is the above an artifact of how puts() is implemented or is it innate in the language spec?

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Re: Lists And Missing Commas
by Tim Daneliuk Dec. 23, 2019

Dec. 23, 2019

On 12/23/19 7:52 PM, DL Neil wrote: > > WebRef: https://docs.python.org/3/reference/lexical_analysis.html Yep, that explains it, but it still feels non-regular to me. From a pointy headed academic POV, I'd like to see behavior consistent across types. Again ... what do I know?

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Lists And Missing Commas
by Tim Daneliuk Dec. 23, 2019

Dec. 23, 2019

If I do this: foo = [ "bar", "baz" "slop", "crud" ] Python silently accepts that and makes the middle term "bazslop". BUT, if I do this: foo = [ "bar", "baz" 1, "crud" ] or this: foo = [ "bar", 2 1, "crud" ] The interpreter throws a syntax error. This is more of an intellectual curiosity than anything else, but why do strings silently concatenate like that, while all other case blow up with an error. i.e., What is about the language the promotes this behavior. At first blush, it seems inconsistent, but what do I know ...

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Transfer a file to httpserver via POST command from curl
by Karthik Sharma Dec. 23, 2019

Dec. 23, 2019

I have written a python server app (actually copied from somewhere) using Flask, that I want to act as a http server. I expect this server to recieve a POST command (of a file) from CURL and save that file on the server. And I should be able to download that file when required. My python scripts are shown below. app.py from flask import Flask UPLOAD_FOLDER = 'home/user/uploads' app = Flask(__name__) #app.secret_key = "secret key" app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER app.config['MAX_CONTENT_LENGTH'] = 16 * 1024 * 1024 main.py import os import urllib.request from app import app from flask import Flask, request, redirect, jsonify from werkzeug.utils import secure_filename ALLOWED_EXTENSIONS = set(['txt', 'pdf', 'png', 'jpg', 'jpeg', 'gif']) def allowed_file(filename): return '.' in filename and filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS @app.route('/file-upload', methods=['POST']) def upload_file(): # check if the post request has the file part if 'file' not in request.files: resp = jsonify({'message' : 'No file part in the request'}) resp.status_code = 400 return resp file = request.files['file'] if file.filename == '': resp = jsonify({'message' : 'No file selected for uploading'}) resp.status_code = 400 return resp if file and allowed_file(file.filename): filename = secure_filename(file.filename) file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename)) resp = jsonify({'message' : 'File successfully uploaded'}) resp.status_code = 201 return resp else: resp = jsonify({'message' : 'Allowed file types are txt, pdf, png, jpg, jpeg, gif'}) resp.status_code = 400 return resp if __name__ == "__main__": app.run() I am doing a POST using curl as follows. curl -X POST --data-binary @/home/user/testfile.txt http:// 127.0.0.1:5000/file-upload Is it really possible to transfer a large binary file from my machine to the above httpserver via POST command and download it again? If yes, is the above Flask app enough for that and what am I doing wrong? Kindly Reply, Regards, Karthik. I am getting 400 Bad Request error from the server. I am new to Flask. What am I doing wrong. Is it possible to transfer a binary file (large) from my computer to the above http server via POST command.? For that purpose is my above code enought? What am I doing wrong?

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Re: Most elegant way to do something N times
by Python Dec. 22, 2019

Dec. 22, 2019

Le 22/12/2019 à 23:50, Stefan Ram a écrit : > Batuhan Taskaya <isidentical(a)gmail.com> writes: >> dont like this for _ in range(n): do() thing. Any suggestions? > > The participants of my beginner classes like to write: > > n * do() > > for that purpose, but usuallythis does not work as intended! > > What would work sometimes is > > eval( n * 'do();' ) > or: class repeatly_do: def __init__(self,n): self.n = n def __mul__(self,action): for _ in range(self.n): action() def do(): print('Here I am...') repeatly_do(5) * do

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