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

EuroPython 2019: Schedule is online
by M.-A. Lemburg June 24, 2019

June 24, 2019

We are pleased to announce the EuroPython 2019 schedule. We will again have more than 130 sessions in total, held by more than 130 speakers. Schedule for EuroPython 2019 * https://ep2019.europython.eu/events/schedule/ * Please note that the schedule may still change in details, but the overall layout is fixed now. Book your EuroPython 2019 Ticket -------------------------------- Please make sure you book your ticket in the coming days. We will switch to late bird rates next week. If you want to attend the training sessions, please buy a training pass in addition to your conference ticket, or get a combined ticket. We only have very few training seats left. Travel & accommodation tips --------------------------- Since we’re close the conference, Basel is in high demand. If you’re having problems finding a hotel, please also consider searching for apartments on the well known booking sites. We have collected a number of recommendations for accommodation and travel to Basel on the EuroPython 2019 website. If you get a hotel or apartment in Basel, you will additionally get a BaselCard for your stay, which allows you to use public transport in Basel for free. Please see our accommodation page for details. Dates and Venues ---------------- EuroPython will be held from July 8-14 2019 in Basel, Switzerland, at the Congress Center Basel (CCB) for the main conference days (Wed-Fri) and the FHNW Muttenz for the workshops/trainings/sprints days (Mon-Tue, Sat-Sun). Tickets can be purchased on our registration page: https://ep2019.europython.eu/registration/buy-tickets/ For more details, please have a look at our website and the FAQ: https://ep2019.europython.eu/faq Help spread the word -------------------- Please help us spread this message by sharing it on your social networks as widely as possible. Thank you ! Link to the blog post: https://blog.europython.eu/post/185811587232/europython-2019-schedule-is-on… Tweet: https://twitter.com/europython/status/1143061849446989824 Enjoy, -- EuroPython 2019 Team https://ep2019.europython.eu/ https://www.europython-society.org/

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generator to write N lines to file
by Sayth Renshaw June 24, 2019

June 24, 2019

Afternoon Trying to create a generator to write the first N lines of text to a file. However, I keep receiving the islice object not the text, why? from itertools import islice fileName = dir / "7oldsamr.txt" dumpName = dir / "dump.txt" def getWord(infile, lineNum): with open(infile, 'r+') as f: lines_gen = islice(f, lineNum) yield lines_gen for line in getWord(fileName, 5): with open(dumpName, 'a') as f: f.write(line) Thanks, Sayth

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Fwd: Understand workflow about reading and writing files in Python
by Windson Yang June 24, 2019

June 24, 2019

Thank you so much for you review DL Neil, it really helps :D. However, there are some parts still confused me, I replyed as below. DL Neil <PythonList(a)danceswithmice.info> 于2019年6月19日周三下午2:03写道： > I've not gone 'back' to refer to any ComSc theory on buffer-management. > Perhaps you might benefit from such? > > I just take a crash course on it so I want to know if I understand the details correctly :D > I like your use of the word "shift", so I'll continue to use it. > > There are three separate units of data to consider - each of which could > be called a "buffer". To avoid confusing (myself) I'll only call the > 'middle one' that: > 1 the unit of data 'coming' from the data-source > 2 the "buffer" you are implementing > 3 the unit of data 'going' out to a data-destination. > > Just to make it clear, when we use `f.write('abc')` in python, (1) means 'abc', (2) means the buffer handle by Python (by default 8kb), (2) means the file *f* we are writing to, right? 1 and 3 may be dictated to you, eg hardware or file specifications, code > requirements, etc. > > So, data is shifted into the (2) buffer in a unit-size decided by (1) - > in most use-cases each incoming unit will be the same size, but remember > that the last 'unit' may/not be full-size. Similarly, data shifted out > from the (2) buffer to (3). > > The size of (1) is likely not that of (3) - otherwise why use a > "buffer"? The size of (2) must be larger than (1) and larger than (2) - > for reasons already illustrated. > Is this a typo? (2) larger than (1) larger than (2)? > > I recall learning how to use buffers with a series of hand-drawn block > diagrams. Recommend you try similarly! > > > Now, let's add a few critiques, as requested (interposed below):- > > > On 19/06/19 3:53 PM, Windson Yang wrote:t > > I'm trying to understand the workflow of how Python read/writes data with > > buffer. I will be appreciated if someone can review it. > > > > ### Read n data > > - may need more than one read operation if the size of (3) "demands" > more data than the size of (1)/one "read". > Looks like the size of len of one read() depends on https://github.com/python/cpython/blob/master/Modules/_io/bufferedio.c#L1655 ? > > > 1. If the data already in the buffer, return data > > - this a data-transfer of size (3) > > For extra credit/an unnecessary complication (but probable speed-up!): > * if the data-remaining is less than size (3) consider a read-ahead > mechanism > > > 2. If the data not in the buffer: > > - if buffer's data-len < size (3) > > > 1. copy all the current data from the buffer > > * if "buffer" is my (2), then no-op > I don't understand your point here, when we read data we would copy some data from the current buffer from python, right? ( https://github.com/python/cpython/blob/master/Modules/_io/bufferedio.c#L1638), we use `out` (which point to res) to store the data here. > > > 2. create a new buffer object, fill the new buffer with raw read > which > > read data from disk. > > * this becomes: perform read operation and append incoming data (size > (1)) to "buffer" - hence why "buffer" is larger than (1), by definition. > NB if size (1) is smaller than size (3), multiple read operations may be > necessary. Thus a read-loop!? > > Yes, you are right, here is a while loop ( https://github.com/python/cpython/blob/master/Modules/_io/bufferedio.c#L1652 ) > > > 3. concat the data in the old buffer and new buffer. > > = now no-op. Hopefully the description of 'three buffers' removes this > confusion of/between buffers. > > I don't get it. When we call the function like seek(0) then read(1000), we can still use the data from buffer from python, right? > > > 4. return the data > > * make the above steps into a while-loop and there won't be a separate > step here (it is the existing step 1!) > > > * build all of the above into a function/method, so that the 'mainline' > only has to say 'give me data'! > > > > ### Write n data > > 1. If data small enough to fill into the buffer, write data to the buffer > > =yes, the data coming from source (1), which in this case is 'your' code > may/not be sufficient to fill the output size (3). So, load it into the > "buffer" (2). > > > 2. If data can't fill into the buffer > > 1. flush the data in the buffer > > =This statement seems to suggest that if there is already some data in > the buffer, it will be wiped. Not recommended! > > We check if any data in the buffer if it does, we flush them to the disk ( https://github.com/python/cpython/blob/master/Modules/_io/bufferedio.c#L1948 ) > =Have replaced the next steps, see below for your consideration:- > > > 1. If succeed: > > 1. create a new buffer object. > > 2. fill the new buffer with data return from raw write > > 2. If failed: > > 1. Shifting the buffer to make room for writing data to the > > buffer > > 2. Buffer as much writing data as possible (may raise > > BlockingIOError) > > 2. return the data > > After above transfer from data-source (1) to "buffer" (2): > > * if len( data in "buffer" ) >= size (3): output > else: keep going > > * output: > shift size(3) from "buffer" to output > retain 'the rest' in/as "buffer" > > NB if the size (2) of data in "buffer" is/could be multiples of size > (3), then the "output" function should/could become a loop, ie keep > emptying the "buffer" until size (2) < size (3). > > > Finally, don't forget the special cases: > What happens if we reach 'the end' (of 'input' or 'output' phase), and > there is still data in (1) or (2)? > Presumably, in "Read" we would discard (1), but in the case of "Write" > we MUST empty "buffer" (2), even if it means the last write is of less > than size (3). > > Yes, you are right, when we are writing data to the buffer and the buffer is full, we have to flush it. NB The 'rules' for the latter may vary between use-cases, eg add > 'stuffing' if the output record MUST be x-bytes long. > > > Hope this helps. > Do you need to hand-code this stuff though, or is there a better way? > I'm trying to write an article for it :D > -- > Regards =dn > -- > https://mail.python.org/mailman/listinfo/python-list Regards Windson

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Python refactoring question and create dynamic attributes
by Arup Rakshit June 23, 2019

June 23, 2019

In the below code: @classmethod def find(self, id): if isinstance(id, list): rows = self.__table__().get_all(*id).run(self.__db__().conn) result = [] for row in rows: acategory = Category() acategory.__dict__.update(row) result.append(acategory) return result else: adict = self.__table__().get(id).run(self.__db__().conn) acategory = Category() acategory.__dict__.update(adict) return acategory I have 2 questions: 1. Is there any better way to create attributes in an object without using __dict__().update() or this is a correct approach? 2. Can we get the same result what for row in rows: block is producing without killing the readability ? To see the context, here is my source code https://gitlab.com/aruprakshit/flask_awesome_recipes/blob/master/app/models… Thanks, Arup Rakshit ar(a)zeit.io

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Re: finding a component in a list of pairs
by Peter Pearson June 23, 2019

June 23, 2019

On 22 Jun 2019 13:24:38 GMT, Stefan Ram <ram(a)zedat.fu-berlin.de> wrote: [snip] > > print( next( ( pair for pair in pairs if pair[ 0 ]== 'sun' ), > ( 0, '(unbekannt)' ))[ 1 ]) > print( next( itertools.dropwhile( lambda pair: pair[ 0 ]!= 'sun', pairs )) > [ 1 ]) [snip] > > The last two lines of the program show two different > approaches to search for the translation of »sun«. > > Which approach is better? Or, do you have yet a better idea > about how to find the translation of »sun« in »pairs«? Are you allowed to use a dict? -- To email me, substitute nowhere->runbox, invalid->com.

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Re: Difference between array( [1,0,1] ) and array( [ [1,0,1] ] )
by edmondo.giovannozzi＠gmail.com June 22, 2019

June 22, 2019

Every array in numpy has a number of dimensions, "np.array" is a function that can create an array numpy given a list. when you write vector_1 = np.array([1,2,1]) you are passing a list of number to thet function array that will create a 1D array. As you are showing: vector_1.shape will return a tuple with the sizes of each dimension of the array that is: (3,) Note the comma thta indicate that is a tuple. While if you write: vector_2 = np.array([[1,2,3]]) You are passing a list of list to the function array that will instruct it to crete a 2D array, even though the size of the first dimension is 1: vector_2.shape (1,3) It is still a tuple as you can see. Try: vector_3 = np.array([[1,2,3],[4,5,6]]) And you'll see that i'll return a 2D array with a shape: vector_3.shape (2,3) As the external list has 2 elements that is two sublists each with 3 elements. The vector_2 case is just when the external list has only 1 element. I hope it is more clear now. Cherrs, Il giorno venerdì 21 giugno 2019 08:29:36 UTC+2, Markos ha scritto: > Hi, > > I'm studying Numpy and I don't understand the difference between > > >>> vector_1 = np.array( [ 1,0,1 ] ) > > with 1 bracket and > > >>> vector_2 = np.array( [ [ 1,0,1 ] ] ) > > with 2 brackets > > The shape of vector_1 is: > > >>> vector_1.shape > (3,) > > But the shape of vector_2 is: > > >>> vector_2.shape > (1, 3) > > The transpose on vector_1 don't work: > > >>> vector_1.T > array([1, 0, 1]) > > But the transpose method in vector_2 works fine: > > >>> vector_2.T > array([[1], > [0], > [1]]) > > > I thought that both vectors would be treated as an matrix of 1 row and 3 > columns. > > Why this difference? > > Any tip? > > Thank you, > Markos

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Difference between array( [1,0,1] ) and array( [ [1,0,1] ] )
by Markos June 21, 2019

June 21, 2019

Hi, I'm studying Numpy and I don't understand the difference between >>> vector_1 = np.array( [ 1,0,1 ] ) with 1 bracket and >>> vector_2 = np.array( [ [ 1,0,1 ] ] ) with 2 brackets The shape of vector_1 is: >>> vector_1.shape (3,) But the shape of vector_2 is: >>> vector_2.shape (1, 3) The transpose on vector_1 don't work: >>> vector_1.T array([1, 0, 1]) But the transpose method in vector_2 works fine: >>> vector_2.T array([[1], [0], [1]]) I thought that both vectors would be treated as an matrix of 1 row and 3 columns. Why this difference? Any tip? Thank you, Markos

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pip vs python -m pip?
by Malcolm Greene June 21, 2019

June 21, 2019

64-bit Python 3.6.8 running on Windows with a virtual environment activated. "pip -v" reports 19.0.3 "python -m pip" reports 19.1.1 Is this behavior by design or a bug? My takeaway is that its better to run "python -m pip ..." vs "pip ..." when running pip related tasks. Thoughts? Malcolm

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How to force "python -m site" ENABLE_USER_SITE to false?
by Malcolm Greene June 21, 2019

June 21, 2019

Any suggestions on how one can force the "python -m site" ENABLE_USER_SITE value to false? Is it possible to globally force this setting - across all users - when installing a system wide version of Python ... or via a command line option when starting a Python session? Motivation: When ENABLE_USER_SITE is true, packages can get accidentally installed in user specific Python\Python3XX\site-packages folder, overriding system packages and ... apparently (at least under Windows) ... virtual environment packages as well. Thank you, Malcolm

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help with python37.dll
by Julia Seacat June 20, 2019

June 20, 2019

Hello, I installed python 3.7 (64 bit) for my Windows computer and am trying to install pip but it is giving me an error that the code execution cannot proceed because python37.dll was not found. How do I install or reinstall this program? Also I already subscribed to the list. Thank you, Julia Julia Seacat [cid:image004.jpg@01D05CB6.58115AC0] 424-269-3800 | 800-718-9853 f | 2321 Rosecrans Avenue, Suite 3270 | El Segundo, CA 90245 | www.terracottagroup.com<http://www.terracottagroup.com/> CONFIDENTIALITY NOTICE and DISCLAIMER: The foregoing is neither an offer nor acceptance concerning any existing agreement. No offer or acceptance is valid as against the Lender unless signed in ink by an authorized officer of the Lender. No email from the Lender shall be deemed to constitute an offer or acceptance concerning any agreement. The Lender intends that there shall be no claims of estoppel and that no person shall change position in reliance upon this correspondence. Nothing in this correspondence is to be construed as a waiver, limitation, or release of any and all rights and remedies of the Lender. This email message is intended only for the person or entity to which it is addressed and may contain confidential and/or privileged material. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. If you are the intended recipient but do not wish to receive communications through this medium, please so advise the sender immediately. Nothing in this communication should be interpreted as a digital or electronic signature that can be used to authenticate a contract or other legal document. In the event this information was obtained in or by the non-intended recipient and/or in error, please contact 424-269-3800 immediately.

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