🌐 Mailman 3 August 2020 - Python-list - python.org

About float/double type number in range.
by ADITYA Aug. 26, 2020

Aug. 26, 2020

Dear Sir/Ma’am I am requesting you to satisfy me about float number in Range function, because in the argument of range we can take integer but not double or float whenever double as well as float are integer in nature but when we use double/float in, it gives error that- “'float' object cannot be interpreted as an integer.” If we want to increment the number by half or quarter what can I do. For ex- Range(1,3,0.5) I want it gives Output as [1 1.5 2 2.5 3) I am requesting to change the nature of increment number nature in above example so that we can increase the number with half or quarter any point value. Your Sincerely Aditya Gautam Saharsa (Bihar) India Postal Code- 852201 Sent from [1]Mail for Windows 10 [2][IMG] Virus-free. [3]www.avg.com References Visible links 1. https://go.microsoft.com/fwlink/?LinkId=550986 2. http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_cam… 3. http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_cam…

7 6

stat_result.st_ino from os.stat isn't constant on a network drive.
by Andrew Nelson Aug. 26, 2020

Aug. 26, 2020

OS: windows 7 Python: 3.8 I am trying to track which files have been modified in a directory on a network mount. When I call the os.stat function for a given file in that directory the stat_result.st_ino changes every time I call it: ``` >>> os.stat('U:\data\current\myfile') os.stat_result(st_mode=33206, st_ino=18446735965107825360, st_dev=33674366, st_nlink=1, st_uid=0, st_gid=0, st_size=433874, st_atime=1598333128, st_mtime=1598330233, st_ctime=1598329773) >>> os.stat('U:\data\current\myfile') os.stat_result(st_mode=33206, st_ino=18446735965183676432, st_dev=33674366, st_nlink=1, st_uid=0, st_gid=0, st_size=433874, st_atime=1598333128, st_mtime=1598330233, st_ctime=1598329773) ``` It's the same file, why on earth does the st_ino field change everytime? st_ino is supposed to "uniquely identify the file for a given value of st_dev." If I do the same thing on a local file instead of on a network mount st_ino is constant and doesn't change. Is this a Python bug, or is it an issue with the way Windows deals with network mounts? Andrew.

2 1

Re: "filterwarnings"
by Peter Otten Aug. 26, 2020

Aug. 26, 2020

Stefan Ram wrote: > I'm not sure I understand "filterwarnings" correctly. > It does not suppress the warning within the "with" statement below. > Outside of the "with" statement, it does work, but according > to sources it also should work within the "with" statement. > > Console transcript: > > |Python 3.9.... > |Type "help", "copyright", "credits" or "license" for more information. > |>>> import warnings > |>>> with warnings.catch_warnings(): > |... warnings.filterwarnings("ignore", category=SyntaxWarning) > |... print( 1 is 1 ) > |... > |<stdin>:3: SyntaxWarning: "is" with a literal. Did you mean "=="? > |True > |>>> warnings.filterwarnings("ignore", category=SyntaxWarning) > |>>> print( 1 is 1 ) > |True > > How could I make "filterwarnings" work inside the "with" statement? > TIA! It does work already: >>> with warnings.catch_warnings(): ... warnings.filterwarnings("ignore", category=UserWarning) ... warnings.warn("yadda") ... >>> warnings.warn("yadda") <stdin>:1: UserWarning: yadda The problem is that you picked the wrong category. As SyntaxWarnings are issued during compilation you need to trigger a compilation to see the effect: >>> with warnings.catch_warnings(): ... warnings.filterwarnings("ignore", category=SyntaxWarning) ... exec("1 is 1") ... >>> exec("1 is 1") <string>:1: SyntaxWarning: "is" with a literal. Did you mean "=="?

1 0

Embedded python: How to debug code in an isolated way
by Eko palypse Aug. 26, 2020

Aug. 26, 2020

Hello, background info first. On windows, python3.8.5 A cpp app has an embedded python interpreter which allows to modify/enhance the cpp app by providing objects to manipulate the cpp app and callbacks to act on certain events, like fileopen, fileclose, updateui ... which are send by the cpp app. The embedded python interpreter acts more or less like the standard python REPL. If you run a script with code like def test(i): print(i*2) test(4) then the test function is now globally available as long as the cpp app is alive. I've written a debugger based on bdb and encountered a situation which I haven't found out how to handle correctly yet. Let's assume I've registered a callback when something changes in the UI. In that case an object function gets called which highlights certain aspects in the UI. Now if I run a script via this debugger it works as long as I don't use the same object function. If I do use it, then the stack gets corrupted(?). For example it look like this stack: <frame at 0x00000000081AB420, file '...\\bdb.py', line 580, code run>, 580 <frame at 0x0000000004CDF550, file '<string>', line 1, code <module>>, 1 <frame at 0x0000000004CD6860, file '...\\test_pydebugger.py', line 8, code <module>>, 8 now if I enter the function which call this object function this gets add <frame at 0x0000000004CEB040, file '\\test_pydebugger.py', line 5, code add_match>, 5 I step through the code and suddenly the stack looks like this <frame at 0x00000000081AB420, file '...\\bdb.py', line 580, code run>, 580 <frame at 0x0000000004CDF550, file '<string>', line 1, code <module>>, 1 <frame at 0x0000000004CD6860, file '...\\test_pydebugger.py', line 8, code <module>>, 8 <frame at 0x0000000007396A40, file '...\\EnhanceAnyLexer.py', line 154, code <lambda>>, 154 <frame at 0x00000000081B35B0, file '...\\EnhanceAnyLexer.py', line 102, code paint_it>, 102)] EnhanceAnyLexer is neither part of the test_pydebugger script nor part of the debugger. It is used to register a callback on the updateui event. So the question is, what do I need to read/learn/understand in order to solve this issue? Or in other words, how can I debug my script in an isolated environment. I can't manipulate the __main__.dict as this seems to have general impact on registered callbacks as well. Any ideas? Thank you Eren

6 10

Whitespace not/required
by dn Aug. 25, 2020

Aug. 25, 2020

Although many new-comers are intrigued by the compulsory indentation rule, I have been surprised to discover that even though whitespace does not usually feature as a formatting-specification, nevertheless Python sometimes requires an absence of whitespace. Will this behavior/requirement continue when using (a pre-release version featuring) the new parser? Whitespace has meaning to us - when it comes to indentation defining (not merely illustrating) blocks of code. However, the rest of the time, it is ignored by Python. (yes, this discussion disdains comments!) For example, whitespace is no problem when it comes to defining a list: month_names = ['Januari', 'Februari', 'Maart', # These are the 'April', 'Mei', 'Juni', # Dutch names... Similarly, a totally blank line will be equally-totally ignored. As my eye-sight ages (it's older than my teeth!), I find code easier to read when there is more whitespace - and it becomes more difficult to parse when whitespace is omitted. For example, I receive regular comments/criticisms for writing an argument list with spaces inside the parentheses, eg def func( arg1, arg2, ): Whilst there are some 'standards' which decry such practice, I note that many IDEs will offer to add such spaces, auto-magically, as a config/option. So, apparently I'm not unique - just 'special'? I don't use 'back-slash continuity' very often (at the expense of more parens!), and was intrigued to discover in experiments; that not only is a space before the back-slash considered optional, but sometimes a space is not necessary at all, eg >>> if\ ... True: print( 'yes' ) ... yes >>> ifTrue: print( 'yes' ) yes although Python won't let me go-crazy: >>> if True andFalse: print( 'yes' ) File "<stdin>", line 1 if True andFalse: print( 'yes' ) ^ SyntaxError: invalid syntax >>> if Tr\ ... ue: print( 'yes' ) File "<stdin>", line 2 if Tr\ ue: print( 'yes' ) ^ SyntaxError: invalid syntax The legal statement: <<<2.1.9. Whitespace between tokens Except at the beginning of a logical line or in string literals, the whitespace characters space, tab and formfeed can be used interchangeably to separate tokens. Whitespace is needed between two tokens only if their concatenation could otherwise be interpreted as a different token (e.g., ab is one token, but a b is two tokens).>>> Thus, (a little later on the same page): <<<One syntactic restriction not indicated by these productions is that whitespace is not allowed between the stringprefix or bytesprefix and the rest of the literal.>>> Thus, it must be expressed as "b'bytes'" and not "b 'bytes'". Admittedly, such separation hadn't occurred to me, in much the same way that "print ()" doesn't seem correct, but... When we break the language-elements into "tokens" the 'bytes' and the argument-list's parentheses are separate from the preceding "b" or function-name, albeit semantically inseparable. For f-strings/formatted string literals, the most usual form is: "{" f_expression ["="] ["!" conversion] [":" format_spec] "}" Remembering that this is BNF, see the space separating the closing-brace from anything preceding it - how else would we separate the components to comprehend? Returning to Python: >>> one = 1 # is the loneliest number... >>> f'{ one }' '1' >>> f'{ one:03 }' Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: Unknown format code '\x20' for object of type 'int' >>> f'{ one:03}' '001' Notice the presence/absence of the final space. >>> pi = 3.14159 # better to import math >>> f'{ pi!r:10 }' Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: Unknown format code '\x20' for object of type 'str' >>> f'{ pi!r:10}' '3.14159 ' >>> f'{ pi!r }' File "<stdin>", line 1 SyntaxError: f-string: expecting '}' >>> f'{ pi!r}' '3.14159' So, the f-string will work if the braces include only an expression surrounded by spaces. However, if one adds a conversion or format-specification, that final space becomes a no-no. Eh what! To be fair, the 'book of words' does say: "A replacement field ends with a closing curly bracket '}'.". No mention of whitespace. No mention that a replacement field consisting only of an f_expression, will be treated differently by allowing a space. Version 3.8 introduced the "=" short-cut: >>> f"{ foo = }" # preserves whitespace " foo = 'bar'" Note the comment! Yet, the manual's examples continue: >>> line = "The mill's closed" >>> f"{line = }" 'line = "The mill\'s closed"' >>> f"{line = :20}" "line = The mill's closed " Hey, why does this second example dispense with the braces-internal spaces? Sure enough, when I check it for myself: >>> line = "The mill's closed" >>> f'{line = :20 }' Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: Unknown format code '\x20' for object of type 'str' >>> f'{ line = :20}' " line = The mill's closed " >>> f'{line = :20}' "line = The mill's closed " Should the closing brace be considered part of a conversion or format-specification? The space (I'd like to add) cannot be considered part of a conversion or format-specification (see BNF, see text of web.ref)! (when you compare how long it took me to (speed) type this message, and how long it took me to figure-out that my 'excess space' was causing a fault in an f-string, the time-cost was about the same. Grrr! (the relative frustrations-caused, somewhat different!) Will be interested in explanations, and improvements to understanding. (but not so much in 'corrections' to my (mis-)behavior - I already pay that price!) If you're operating at the 'bleeding edge', will be interested to hear how the 'new parser' handles same. Web.Ref: https://docs.python.org/3/reference/lexical_analysis.html -- Regards, =dn

2 1

Training Review: Computational Thinking for Problem Solving
by dn Aug. 24, 2020

Aug. 24, 2020

Many of us learn Python by memorising code-constructs and their use. Even over-coming this learning-curve is but a small portion of becoming a competent coder or programmer. The challenges of learning how to construct an algorithm, and/or how to analyse a real-world problem to produce a solution, are not to be found in the Python Tutorial. However, such higher-order problems often surface on the Python-Tutor and Python Discussion Lists. For newcomers (and anyone in the field who would like to fill-in topics 'missing' in his/her basic understanding), Coursera offer a "Computational Thinking for Problem Solving" course (free* or $certified) from "Penn" (University of Pennsylvania, USA). I have occupied various 'spare' moments during the last week or so, to review the course, and am recommend it to you/yours. Aside from coders, you might also mention it to any friends who want to learn 'problem-solving' (an increasingly important skill in these modern-times where the only constant is 'change') because this is not a 'computer course'. Starting at higher-level thinking, gradually more detail is added, before arriving at the level of implementing computer-based solutions in Python. It offers a (rather brief) introduction to Python. Thus could be used as a 'taster', before moving to Python-for-the-sake-of-Python course. Throughout the course reference is made to case-studies drawn from the university's wider operations. There is also an interesting topic in linguistic analysis (ie the stuff of grammar-checkers, search engines, etc) which trainees can gradually develop, stage-by-stage. Here is their introduction:- <<< Computational thinking is the process of approaching a problem in a systematic manner and creating and expressing a solution such that it can be carried out by a computer. But you don't need to be a computer scientist to think like a computer scientist! In fact, we encourage students from any field of study to take this course. Many quantitative and data-centric problems can be solved using computational thinking and an understanding of computational thinking will give you a foundation for solving problems that have real-world, social impact. In this course, you will learn about the pillars of computational thinking, how computer scientists develop and analyze algorithms, and how solutions can be realized on a computer using the Python programming language. By the end of the course, you will be able to develop an algorithm and express it to the computer by writing a simple Python program. This course will introduce you to people from diverse professions who use computational thinking to solve problems. You will engage with a unique community of analytical thinkers and be encouraged to consider how you can make a positive social impact through computational thinking. >>> 100% online Flexible deadlines Beginner Level Approx. 17 hours to complete Four 'weeks' or sessions: Pillars of Computational Thinking Expressing and Analyzing Algorithms Fundamental Operations of a Modern Computer Applied Computational Thinking Using Python https://www.coursera.org/learn/computational-thinking-problem-solving#sylla… They did conclude by uttering heresy: that graduates might like to move to "more advanced languages like Java ... JavaScript", but let's not hold that lapse of judgement against them (they are after-all, a school of Engineering)! * the $free option allows access to quizzes, tests, and assignments but not to any grading process. That said, any 'problems', phrased with at a Python background, could likely be discussed/corrected in posts to the Python-Tutor List (don't forget to declare the course and notify which session/component). Disclaimer: I use the ('competing') edX training/education platform - but for non-Python courses. -- Regards, =dn

1 0

Re: There is LTS?
by soyeomul＠doraji.xyz Aug. 24, 2020

Aug. 24, 2020

Léo El Amri <leo(a)superlel.me> writes: > On 24/08/2020 04:54, 황병희 wrote: >> Hi, just i am curious. There is LTS for *Python*? If so, i am very thank >> you for Python Project. > > Hi Byung-Hee, > > Does the "LTS" acronym you are using here stands for "Long Term Support" ? > > If so, then the short answer is: Yes, kind of. There is a 5 years > maintenance for each major version of Python 3. > > You can find information on how Python is released and maintained at PEP > 101 [1] and on the developers documentation [2]. > > Each major Python release typically have a PEP associated with it where > past minor releases dates and future plans are recorded. > For example: PEP 494 [3] for Python 3.6, PEP 537 [4] for Python 3.7 and > PEP 569 [5] for Python 3.8. > > [1] https://www.python.org/dev/peps/pep-0101/ > [2] https://devguide.python.org/devcycle/ > [3] https://www.python.org/dev/peps/pep-0494/ > [4] https://www.python.org/dev/peps/pep-0537/ > [5] https://www.python.org/dev/peps/pep-0569/ Wow Léo you nice guy!!! Thank You!!! Sincerely, Byung-Hee -- ^고맙습니다 _救濟蒼生_ 감사합니다_^))//

1 0

Program chaining on Windows
by Rob Cliffe Aug. 24, 2020

Aug. 24, 2020

On WIndows 10, running Python programs in a DOS box, I would like one Python program to chain to another. I.e. the first program to be replaced by the second (*not* waiting for the second to finish, as with e.g. os.system). This doesn't seem a lot to ask, but so far I have been unable to so this. I am using Python 3.8.3. Some attempts so far (may be nonsensical): ATTEMPT #1 ---------------- # File X1.py import os print("This is X1") os.execl('C:\\Python38\\python.exe', 'X2.py') # File X2.py print("This is X2") When I type "X1.py", it prints "This is X1", then starts the Python interactive interpreter. Furthermore: TLDR: Weird behaviour Long version: If I attempt to exit the interpreter with ctl-Z, this apparently succeeds (displaying the Windows command prompt), but in reality it is still in the interpreter, e.g. if I type "dir" it responds "<built-in function dir>" followed by the ">>>" interpreter prompt. And this cycle (ctl-Z etc.) can be repeated ad nauseam. If instead I try to exit from the interpreter with "exit()", the cursor moves to the next line and the interpreter waits for more input (but without displaying the prompt). If I try "exit()" again, the whole DOS box disappears. ATTEMPT #2 ----------------- # File X1.py import os print("This is X1") os.execl("C:\\Python38\\python.exe X2.py", '') This raises ValueError: execv() arg 2 first element cannot be empty ATTEMPT #3 ---------------- import os, sys print("This is X1") os.execl("%s X2.py" % sys.executable, "X2.py") This raises FileNotFoundError: [Errno 2] No such file or directory ATTEMPT #4 ---------------- # File X1.py import os, sys print("This is X1") os.execv(sys.executable, ['X2.py']) This behaves the same as, or similarly to, Attempt #1. ATTEMPT #5 ---------------- # File X1.py import os print("This is X1") os.popen('python X2.py') # File X2.py as previously TLDR: Really weird behaviour! Long version: If I type "X1.py", it displays "This is X1" followed by the DOS prompt. If I type in a DOS command, it is executed, and the DOS prompt displayed. However, if I type in another DOS command, nothing happens except that the cursor moves to the next line and waits for input (no prompt). If I type in a further DOS command, it is executed. If I type still another DOS command, I see Exception ignored in: <io.TextIOWrapper name='<stdout>' mode='w' encoding='cp1252'> OSError: [Errno 22] Invalid argument and the cursor moves to the next line (no prompt). If I type in one more DOS command, it is executed, and we appear to be back to normal DOS operation. ATTEMPT #6 ----------------- # File X1.py import subprocess, sys print("This is X1") subprocess.Popen('X2.py', executable=sys.executable) This behaves the same as, or similarly to, Attempt #1. ATTEMPT #7 ----------------- # File X1.py import subprocess, sys print("This is X1") subprocess.Popen('-c X2.py', executable=sys.executable) # added -c # File X2.py print("This is X2") Some progress (maybe). This prints "This is X1", then the DOS prompt followed by "This is X2", then the cursor moves to the next line and sits waiting for input (no prompt). If I then type something in, this is interpreted as a DOS command, and finally the DOS prompt is displayed. To find out more about what is happening: ATTEMPT #8 ---------------- # File X1.py as above # File X2.py print("This is X2") input("Press Enter to continue X2") input("Press Enter to quit X2") If I type "X1.py", it displays: This is X1 C:\Python38>This is X2 Press Enter to continue X2 Now: TLDR: More weird behaviour, as if Windows and X2.py were taking turns to collect lines from the console. Long version: Now if I type something in and press Enter, it is interpreted as a *DOS command". Then the DOS prompt is displayed. Now if I (type something and) hit Enter, I see Press Enter to quit X2 Now if I type something and hit Enter, it is interpreted as a DOS command, and the DOS prompt is displayed again. Now if I type in a DOS command and press Enter, it is ignored but the cursor moves to the next line and waits for input (no prompt). Now if I type another DOS command, it is executed. Finally we appear to be done (the DOS prompt is displayed and we are back to normal DOS operation). Am I missing something? Is there a way in Windows for one Python program to "chain" to another (or indeed to any executable) without waiting for the latter to finish? Thanks in advance Rob Cliffe

7 17

Issue in installing Python (Windows 10)
by Debasis Chatterjee Aug. 24, 2020

Aug. 24, 2020

---------- Forwarded message --------- From: Debasis Chatterjee <debchat1955(a)gmail.com> Date: Sun, Aug 23, 2020 at 11:06 AM Subject: Issue in installing Python (Windows 10) To: <python-list(a)python.org> Hi I started off by using "python-3.8.5.exe". I use "Run as Administrator" option to click this (provide my local-admin username/pwd). After this, I see python shell available. But no IDLE. Not sure why? >From CMD, I can check "pip list". Surprisingly, it shows me packages that I installed earlier, before deinstalling and reinstalling. I am doing all these steps because earlier my program could not see installed packages although I could see using "pip list". Something is not right. Hence I am trying to make a fresh restart. One thing odd is that even after removing installed program (Python) from control panel, I still find that from "Start". Please help. Thank you Debasis Chatterjee

2 1

ANN: Version 0.1.6 of sarge (a subprocess wrapper library) has been released.
by Vinay Sajip Aug. 24, 2020

Aug. 24, 2020

Version 0.1.6 of Sarge, a cross-platform library which wraps the subprocess module in the standard library, has been released. What changed? ------------- - Fixed #44: Added an optional timeout to Command.wait() and Pipeline.wait(), which only takes effect on Python >= 3.3. - Fixed #47: Added the ``replace_env`` keyword argument which allows a complete replacement for ``os.environ`` to be passed. - Fixed #51: Improved error handling around a Popen call. What does Sarge do? ------------------- Sarge tries to make interfacing with external programs from your Python applications easier than just using subprocess alone. Sarge offers the following features: * A simple way to run command lines which allows a rich subset of Bash- style shell command syntax, but parsed and run by sarge so that you can run on Windows without cygwin (subject to having those commands available): >>> from sarge import capture_stdout >>> p = capture_stdout('echo foo | cat; echo bar') >>> for line in p.stdout: print(repr(line)) ... 'foo\n' 'bar\n' * The ability to format shell commands with placeholders, such that variables are quoted to prevent shell injection attacks. * The ability to capture output streams without requiring you to program your own threads. You just use a Capture object and then you can read from it as and when you want. * The ability to look for patterns in captured output and to interact accordingly with the child process. Advantages over subprocess --------------------------- Sarge offers the following benefits compared to using subprocess: * The API is very simple. * It's easier to use command pipelines - using subprocess out of the box often leads to deadlocks because pipe buffers get filled up. * It would be nice to use Bash-style pipe syntax on Windows, but Windows shells don't support some of the syntax which is useful, like &&, ||, |& and so on. Sarge gives you that functionality on Windows, without cygwin. * Sometimes, subprocess.Popen.communicate() is not flexible enough for one's needs - for example, when one needs to process output a line at a time without buffering the entire output in memory. * It's desirable to avoid shell injection problems by having the ability to quote command arguments safely. * subprocess allows you to let stderr be the same as stdout, but not the other way around - and sometimes, you need to do that. Python version and platform compatibility ----------------------------------------- Sarge is intended to be used on any Python version >= 2.6 and is tested on Python versions 2.6, 2.7, 3.3, 3.4, 3.5, 3.6, 3.7 and 3.8 on Linux, Windows, and Mac OS X (not all versions are tested on all platforms, but sarge is expected to work correctly on all these versions on all these platforms). Finding out more ---------------- You can read the documentation at http://sarge.readthedocs.org/ There's a lot more information, with examples, than I can put into this post. You can install Sarge using "pip install sarge" to try it out. The project is hosted on BitBucket at https://bitbucket.org/vinay.sajip/sarge/ And you can leave feedback on the issue tracker there. I hope you find Sarge useful! Regards, Vinay Sajip

1 0