Python information and short questions megathread.

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Hammerite: Mar 9, 2007; And you don't remember what I said here, either, but it was pompous and stupid.; Jade Ear Joe

code:

while searchLength > 0:
	if cleanString[searchLength] == cleanString[-searchLength]:
		searchLength -= 1
	else:
		return False
	return True

is equivalent to

code:

while searchLength > 0:
	if cleanString[searchLength] == cleanString[-searchLength]:
		searchLength -= 1
		return True
	else:
		return False

is equivalent (given that searchLength is local) to

code:

while searchLength > 0:
	if cleanString[searchLength] == cleanString[-searchLength]:
		return True
	else:
		return False

is equivalent to

code:

while searchLength > 0:
	return cleanString[searchLength] == cleanString[-searchLength]

# ? Oct 13, 2015 09:31

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# ? May 8, 2024 10:23

Xeno54: Apr 25, 2004; bread

Xeno54 posted:

The "return True" is over indented and inside the while loop, so your code will either return True or False on the first iteration (see Hammerite's analysis). You should be good if you remove an indent and have "return True" at the same level as the while loop.

i thought i tried that, huh. so if i do that, then 'while the counter is whatever if comparison is still valid deincrement searchLength and try again' is the expected behavior?

e: haha, that was the correct placement of the return in my previous test, but i forgot to test for str[index] == str[index-1]], and one of my test words was 'banana', which is a valid offset palindrome under that logic...

boner confessor fucked around with this message at 15:57 on Oct 13, 2015

# ? Oct 13, 2015 15:47

Suspicious Dish: Sep 24, 2011; 2020 is the year of linux on the desktop, bro; Fun Shoe

Perhaps you want some more practice with loops, but, reminder: a palindrome is a word that is the same forwards and backwards.

# ? Oct 13, 2015 16:01

lord of the files: Sep 4, 2012

SurgicalOntologist posted:

This my first foray into scraping Javascript pages, and I'm trying to use dryscrape which is based on QT webkit. If everything is working correctly I should be triggering a "download file" popup. How do I catch the file the site is trying to send me, ideally into a string but I would be happy reading it again off the local file system.

is your download being triggered by redirecting you to another page? if it is, you can extract the url from the previous page with dryscape and parse the download link out of that, then use python's HTTP library to load the binary data into a string, such as this:

code:

my_silly_file = urllib2.urlopen(extracted_dryscape_url).read()

dryscape is a web parser and does not have any functions to handle downloading of files, so you will have to use something external to it to download your data.

# ? Oct 13, 2015 17:40

chutwig: May 28, 2001; BURLAP SATCHEL OF CRACKERJACKS

Nitrocat posted:

is your download being triggered by redirecting you to another page? if it is, you can extract the url from the previous page with dryscape and parse the download link out of that, then use python's HTTP library to load the binary data into a string, such as this:
code:
my_silly_file = urllib2.urlopen(extracted_dryscape_url).read()
dryscape is a web parser and does not have any functions to handle downloading of files, so you will have to use something external to it to download your data.

I used Chrome dev tools to find the POST that generates the data, but it includes a whole lot of json. I tried copy-pasting it from Chrome and keep getting JavaScript errors. I still need to try copy-pasting the headers as well. But I'm wondering if it would be possible to use dryscrape or a similar tool to get the POST payload that gets sent when I click the "download" button. Then I send that payload through requests.

# ? Oct 14, 2015 04:57

Suspicious Dish: Sep 24, 2011; 2020 is the year of linux on the desktop, bro; Fun Shoe

SurgicalOntologist posted:

I can't resist, even though Suspicious Dish already hinted at it in a much more pedagogical manner. But here's my solution:
Python code:
def is_palindrome(x):
    return ''.join(reversed(x)) == x

Python code:

def is_palindrome(x):
    return x == x[::-1]

Is what I usually see for idiomatic Python.

# ? Oct 14, 2015 06:19

KICK BAMA KICK: Mar 2, 2009

Suspicious Dish posted:

Python code:
def is_palindrome(x):
    return x == x[::-1]
Is what I usually see for idiomatic Python.

Yeah, that (with any sanitization you want like .lower()) is what I'd call the most idiomatic.

# ? Oct 14, 2015 06:34

Cingulate: Oct 23, 2012; by Fluffdaddy

In matplotlib, I want to create axes at arbitrary positions who share size and yaxis/xaxis with some other axis.
That is, I have created an axis, and now I want to create another axis at another position with the same extent, but different origin.

I do not see an elegant way of doing this. Any tips?

# ? Oct 14, 2015 13:04

Munkeymon: Aug 14, 2003; Motherfucker's got an
armor-piercing crowbar! Rigoddamndicu𝜆ous.

SurgicalOntologist posted:

I used Chrome dev tools to find the POST that generates the data, but it includes a whole lot of json. I tried copy-pasting it from Chrome and keep getting JavaScript errors. I still need to try copy-pasting the headers as well. But I'm wondering if it would be possible to use dryscrape or a similar tool to get the POST payload that gets sent when I click the "download" button. Then I send that payload through requests.

In the Netowrk tab of the Chrome dev tools, you can copy the request as a cURL command which will include the headers. You can also just copy the headers to see what's being sent and incorporate that into a urllib request.

# ? Oct 14, 2015 14:29

BannedNewbie: Apr 22, 2003; HOW ARE YOU? -> YOSHI?
FINE, THANK YOU. -> YOSHI.

Cingulate posted:

In matplotlib, I want to create axes at arbitrary positions who share size and yaxis/xaxis with some other axis.
That is, I have created an axis, and now I want to create another axis at another position with the same extent, but different origin.

I do not see an elegant way of doing this. Any tips?

Do you have an example of the kind of figure you are trying to create?
My guess of the way to approach this is to create another subplot with the same axis size, and the use subplot2grid() to move it where you want.

# ? Oct 14, 2015 18:59

Tacos Al Pastor: Jun 20, 2003

Im not sure I get virtualenv. I tried to install Flask on my Mac per the instructions, but the default is to run 2.7.10 whereas I'm using 3.2. Anyone know how to fix this?

# ? Oct 14, 2015 19:00

Cingulate: Oct 23, 2012; by Fluffdaddy

BannedNewbie posted:

Do you have an example of the kind of figure you are trying to create?
My guess of the way to approach this is to create another subplot with the same axis size, and the use subplot2grid() to move it where you want.

The problem is mainly, how do I know the first axes' size?

# ? Oct 14, 2015 20:12

OnceIWasAnOstrich: Jul 22, 2006

spiralbrain posted:

Im not sure I get virtualenv. I tried to install Flask on my Mac per the instructions, but the default is to run 2.7.10 whereas I'm using 3.2. Anyone know how to fix this?

You will have installed virtualenv as a package of some Python. If you then use virtualenv to create a virtual environment, by default it will create a venv for the Python that it is installed to. Python 2.7.10 is the system Python for new versions of OSX, so I am guessing you installed virtualenv to that Python instead of your 3.2 (simply installing 3.2 will not overwrite the system Python and the system Python remains the default unless you specifically change your PATH variable). You can still use this virtualenv with Python 3.3 by specifying which interpreter you want when you create the venv, something like virtualenv -p /usr/local/bin/python3 mypy32env.

# ? Oct 14, 2015 20:23

BannedNewbie: Apr 22, 2003; HOW ARE YOU? -> YOSHI?
FINE, THANK YOU. -> YOSHI.

Cingulate posted:

The problem is mainly, how do I know the first axes' size?

Again, it would be easier to help you out if I had a clear understanding of what you're trying to do, but something like this might work:

code:

# first set of axes
ax = plt.subplot2grid((2,2),(0, 0))
plt.plot(stuff)
# grab the dimensions of your first plot
x_dimensions = plt.xlim()
y_dimensions = plt.ylim()

# second set of axes
ax = plt.subplot2grid((2,2),(0,1))
plt.plot(more_stuff)
plt.xlim(x_dimensions)
plt.ylim(y_dimensions)

# ? Oct 14, 2015 21:52

chutwig: May 28, 2001; BURLAP SATCHEL OF CRACKERJACKS

Suspicious Dish posted:

Python code:
def is_palindrome(x):
    return x == x[::-1]
Is what I usually see for idiomatic Python.

the magnificent burn of being ultra code golfed

# ? Oct 14, 2015 23:31

Gangsta Lean: Dec 3, 2001; Calm, relaxed...what could be more fulfilling?

That isn't code golf at all. That is indeed the most straightforward way to test a palindrome in any language.
1. Create a reversed copy of the original string.
2. Compare the copy to the original, testing for equality.

It just so happens that the idiomatic way to reverse a string in Python is short and somewhat cryptic.

# ? Oct 15, 2015 02:03

Tacos Al Pastor: Jun 20, 2003

OnceIWasAnOstrich posted:

You will have installed virtualenv as a package of some Python. If you then use virtualenv to create a virtual environment, by default it will create a venv for the Python that it is installed to. Python 2.7.10 is the system Python for new versions of OSX, so I am guessing you installed virtualenv to that Python instead of your 3.2 (simply installing 3.2 will not overwrite the system Python and the system Python remains the default unless you specifically change your PATH variable). You can still use this virtualenv with Python 3.3 by specifying which interpreter you want when you create the venv, something like virtualenv -p /usr/local/bin/python3 mypy32env.

This helps. Thank you. I want the virtualenv to be used for Python 3.X (forget which version is loaded on my other laptop) so yeah, currently its not pointed at that and I could see it was giving me a path error for the Flask import when I tried running the basic Flask hello world app so I figured something in the virtualenv wasn't setup correctly. Thanks for that command.

I'm still not exactly sure how the virtual workspace works but it seems as though it makes it easier to switch between 2.7 and 3.x depending on which version you want to work with...also something with dependencies, but thats about all I know. Def need to read up more on this.

# ? Oct 15, 2015 03:10

Proteus Jones: Feb 28, 2013

spiralbrain posted:

This helps. Thank you. I want the virtualenv to be used for Python 3.X (forget which version is loaded on my other laptop) so yeah, currently its not pointed at that and I could see it was giving me a path error for the Flask import when I tried running the basic Flask hello world app so I figured something in the virtualenv wasn't setup correctly. Thanks for that command.

I'm still not exactly sure how the virtual workspace works but it seems as though it makes it easier to switch between 2.7 and 3.x depending on which version you want to work with...also something with dependencies, but thats about all I know. Def need to read up more on this.

You may want to look into Anaconda Python. I really like conda for creating environments.

code:

conda create -n my_flask
source activate my_flask
conda install flask [additional package] [additional package]

This will create a conda environment with only the packages you need. Conda will figure out all the dependancies flask needs and install those as well. Another nice thing is I can keep the environment using the versions I need for my package dependancies. I'm still playing around with "conda build" so I can bundle up my environments and easily get them set up on the systems I need them.

Another nice thing is I can point PyCharm to the environment directory, and it will take it from there automatically using the conda environment on a project by project basis.

# ? Oct 15, 2015 04:05

boner confessor: Apr 25, 2013; by R. Guyovich

both of these just flip the string and test that against the input, right? i figured that was more efficient but i wanted to do a step by step comparison

SurgicalOntologist posted:

Python code:

def is_palindrome(x):
    return ''.join(reversed(x)) == x

return is a built in function that produces a bool
'' creates a new empty string?
.join fills in the new string with the reversed input x
== x tests to see if this new string is the same as the input string

Python code:

def is_palindrome(x):
    return x == x[::-1]

and this does the same thing, except using string slicing to start from the end and work backwards at an interval of 1 char per char, effectively reversing the string?

thanks all

# ? Oct 15, 2015 06:28

QuarkJets: Sep 8, 2008

quote:

Python code:
def is_palindrome(x):
    return x == x[::-1]
and this does the same thing, except using string slicing to start from the end and work backwards at an interval of 1 char per char, effectively reversing the string?

thanks all

That's right

# ? Oct 15, 2015 11:58

SurgicalOntologist: Jun 17, 2004

In Python 3 at least you do need to call join, because reversed returns a special iterator object. join with an empty string essentially concatenates any iterator of strings.

# ? Oct 15, 2015 13:34

Roargasm: Oct 21, 2010; Hate to sound sleazy
But tease me
I don't want it if it's that easy

Recursively you could do:

code:

str = "racecar"
str = str.lower()

def isPal(s):
    if len(s) <= 1:
        return True

    else:
        answer = s[0] == s[-1] and isPal(s[1:-1])
        return answer

print isPal(str)

# ? Oct 15, 2015 15:24

No Safe Word: Feb 26, 2005

Roargasm posted:

Recursively you could do:

code:

str = "racecar"
str = str.lower()

def isPal(s):
    if len(s) <= 1:
        return True

    else:
        answer = s[0] == s[-1] and isPal(s[1:-1])
        return answer

print isPal(str)

Pro tip: don't name variables str (or list or int, etc.)

# ? Oct 15, 2015 15:53

vodkat: Jun 30, 2012; cannot legally be sold as vodka

Whats the neatest way to sort a list of integers into other lists? At the moment I've got something and its working fine, but I'm sure its probably a really inefficient way to solve this problem.

code:

for x in pricesort:
    if x >= 50000000:
        fiftymil.append(x)
    if x >=45000000 and x <= 50000000:
        fourtyfivemil.append(x)

and so on all the way down to zero. Obviously this takes up a ridiculous amount of lines for a relatively simply operation so I wondering how else it could be done.

# ? Oct 15, 2015 15:56

Thots and Prayers: Jul 13, 2006; A is the for the atrocious abominated acts that YOu committed. A is also for ass-i-nine, eight, seven, and six.

B, b, b - b is for your belligerent, bitchy, bottomless state of affairs, but why?

C is for the cantankerous condition of our character, you have no cut-out.; Grimey Drawer

vodkat posted:

Whats the neatest way to sort a list of integers into other lists? At the moment I've got something and its working fine, but I'm sure its probably a really inefficient way to solve this problem.
code:
for x in pricesort:
    if x >= 50000000:
        fiftymil.append(x)
    if x >=45000000 and x <= 50000000:
        fourtyfivemil.append(x)
and so on all the way down to zero. Obviously this takes up a ridiculous amount of lines for a relatively simply operation so I wondering how else it could be done.

Something something integer division. x//5M will equal 9 for 45M-49999999, 8 for 40M-44999999, 7 for 35M-39999999 and etc. If you had a list of lists, you could use the 9,8,7,6 to select the proper list.

# ? Oct 15, 2015 16:14

No Safe Word: Feb 26, 2005

vodkat posted:

Whats the neatest way to sort a list of integers into other lists? At the moment I've got something and its working fine, but I'm sure its probably a really inefficient way to solve this problem.
code:
for x in pricesort:
    if x >= 50000000:
        fiftymil.append(x)
    if x >=45000000 and x <= 50000000:
        fourtyfivemil.append(x)
and so on all the way down to zero. Obviously this takes up a ridiculous amount of lines for a relatively simply operation so I wondering how else it could be done.

My python is super rusty so this may not be very pythonic or even that efficient but

code:

>>> def segment(nums, segment_size):
...     results = []
...     sorted_nums = sorted(nums)
...     for upper in range(segment_size, max(nums), segment_size):
...             results.append([])
...             x = sorted_nums[0]
...             while x < upper:
...                     results[-1].append(x)
...                     sorted_nums.remove(x)
...                     x = sorted_nums[0]
...     results.append(sorted_nums)
...     return results
>>> nums = [random.randint(0, 1000) for _ in range(100)]
>>> nums
[154, 457, 937, 456, 947, 278, 763, 151, 266, 165, 379, 783, 261, 795, 723, 312, 464, 139, 215, 793, 560, 914, 816, 677, 57,
84, 977, 856, 217, 991, 762, 328, 545, 860, 520, 767, 697, 750, 294, 232, 134, 190, 48, 111, 337, 751, 243, 353, 738, 951, 370,
116, 815, 401, 48, 688, 614, 824, 894, 643, 591, 756, 358, 772, 134, 797, 522, 856, 612, 413, 323, 231, 104, 425, 153, 352,
347, 690, 573, 223, 74, 706, 379, 484, 588, 935, 389, 67, 228, 397, 43, 559, 227, 86, 737, 738, 832, 819, 898, 495]
>>> segment(nums, 10)
[[], [], [], [], [43, 48, 48], [57], [67], [74], [84, 86], [], [104], [111, 116], [], [134, 134, 139], [], [151, 153, 154], [165], [], [], [190], [], [215,
217], [223, 227, 228], [231, 232], [243], [], [261, 266], [278], [], [294], [], [312], [323, 328], [337], [347], [352, 353, 358], [], [370, 379,
379], [389], [397], [401], [413], [425], [], [], [456, 457], [464], [], [484], [495], [], [], [520, 522], [], [545], [559], [560], [573], [588], [591], [],
[612, 614], [], [], [643], [], [], [677], [688], [690, 697], [706], [], [723], [737, 738, 738], [], [750, 751, 756], [762, 763, 767], [772], [783],
[793, 795, 797], [], [815, 816, 819], [824], [832], [], [856, 856], [860], [], [], [894, 898], [], [914], [], [935, 937], [947], [951], [], [977], [], [991]]
>>> segment(nums, 100)
[[43, 48, 48, 57, 67, 74, 84, 86], [104, 111, 116, 134, 134, 139, 151, 153, 154, 165, 190], [215, 217, 223, 227, 228, 231, 232, 243, 261, 266, 278, 294],
[312, 323, 328, 337, 347, 352, 353, 358, 370, 379, 379, 389, 397], [401, 413, 425, 456, 457, 464, 484, 495], [520, 522, 545, 559, 560, 573, 588, 591],
[612, 614, 643, 677, 688, 690, 697], [706, 723, 737, 738, 738, 750, 751, 756, 762, 763, 767, 772, 783, 793, 795, 797], [815, 816, 819, 824, 832, 856, 856,
860, 894, 898], [914, 935, 937, 947, 951, 977, 991]]

This will obviously create a shitload of empty lists if your resultset is sparse, in which case you could cull the empty lists or use a dict if you wanted (would make the -1 go away). Also it doesn't preserve ordering obviously.

e: forgot to append the leftovers, fixed

No Safe Word fucked around with this message at 16:23 on Oct 15, 2015

# ? Oct 15, 2015 16:19

SurgicalOntologist: Jun 17, 2004

vodkat posted:

Whats the neatest way to sort a list of integers into other lists? At the moment I've got something and its working fine, but I'm sure its probably a really inefficient way to solve this problem.
code:
for x in pricesort:
    if x >= 50000000:
        fiftymil.append(x)
    if x >=45000000 and x <= 50000000:
        fourtyfivemil.append(x)
and so on all the way down to zero. Obviously this takes up a ridiculous amount of lines for a relatively simply operation so I wondering how else it could be done.

You should be using numpy.

Python code:

pricesort = np.asarray(pricesort)
fiftymil = pricesort[pricesort >= 50000000]
fourtyfivemil = pricesort[(pricesort >= 45000000) & (pricesort < 50000000)]

# ? Oct 15, 2015 16:41

Hammerite: Mar 9, 2007; And you don't remember what I said here, either, but it was pompous and stupid.; Jade Ear Joe

SurgicalOntologist posted:

You should be using numpy.

Overkill for something so basic that can easily be done just using Python.

Python code:

def sort_into_bins (iterable, bin_interval_size):
    from collections import defaultdict
    lists = defaultdict(lambda: [])
    for item in iterable:
        lists[bin_interval_size * (item // bin_interval_size)].append(item)
    return lists

sorted_items = sort_into_bins(pricesort, 5000000)

# ? Oct 15, 2015 19:00

SurgicalOntologist: Jun 17, 2004

Hammerite posted:

Overkill for something so basic that can easily be done just using Python.

That's fair, if it's really just this one thing. But someone who can benefit from array indexing once is likely to benefit from it in other places as well.

# ? Oct 15, 2015 19:33

QuarkJets: Sep 8, 2008

SurgicalOntologist posted:

In Python 3 at least you do need to call join, because reversed returns a special iterator object. join with an empty string essentially concatenates any iterator of strings.

# ? Oct 15, 2015 19:35

QuarkJets: Sep 8, 2008

Hammerite posted:

Overkill for something so basic that can easily be done just using Python.

Python code:

def sort_into_bins (iterable, bin_interval_size):
    from collections import defaultdict
    lists = defaultdict(lambda: [])
    for item in iterable:
        lists[bin_interval_size * (item // bin_interval_size)].append(item)
    return lists

sorted_items = sort_into_bins(pricesort, 5000000)

Numpy is Python

# ? Oct 15, 2015 19:37

chutwig: May 28, 2001; BURLAP SATCHEL OF CRACKERJACKS

QuarkJets posted:

Numpy is Python

Probably what he means is "can be done with the Python standard library without needing to install anything".

# ? Oct 15, 2015 23:48

Nippashish: Nov 2, 2005; Let me see you dance!

chutwig posted:

Probably what he means is "can be done with the Python standard library without needing to install anything".

I don't understand, why would you install python without installing numpy?

# ? Oct 16, 2015 08:40

Hammerite: Mar 9, 2007; And you don't remember what I said here, either, but it was pompous and stupid.; Jade Ear Joe

Nippashish posted:

I don't understand, why would you install python without installing numpy?

Because it's the path of least resistance to just install standard Python, and you don't need to do things that numpy is designed to do (i.e. intensive number-crunching)?

I had just python installed on my machines for ages. Recently I installed another Python distribution that has numpy included because I wanted to play around with a neural network library, and I concluded from reading about the amount of matrix maths involved that it would be needed (and besides the library I wanted to use had it as a dependency). If I hadn't been looking at that then I still wouldn't have it installed because day-to-day I don't really use Python to do number-crunching, just to script stuff, and it's fast enough for that purpose.

# ? Oct 16, 2015 11:15

Thermopyle: Jul 1, 2003; ...the stupid are cocksure while the intelligent are full of doubt. �Bertrand Russell

Nippashish posted:

I don't understand, why would you install python without installing numpy?

Because the vast majority of things people do with Python get no particular benefit out of numpy?

# ? Oct 16, 2015 14:49

vikingstrike: Sep 23, 2007; whats happening, captain

Thermopyle posted:

Because the vast majority of things people do with Python get no particular benefit out of numpy?

This. When I first started using python I had no needs outside of the standard library, but once I started doing my data analysis/cleaning/plotting in python I moved over to the Anaconda distribution since pandas, numpy, and MPL are daily drivers for me now. Once of the things I loved as a beginner to the language was how robust (at least to me) the standard library was in helping me do what I needed.

# ? Oct 16, 2015 15:12

lord of the files: Sep 4, 2012

Thermopyle posted:

Because the vast majority of things people do with Python get no particular benefit out of numpy?

correct. the majority of python users don�t have much of a user for libraries like numpy, matplotlip, panda�s, etc. the standard library is robust enough for what most developers need. i use those libs for data plotting and statistical analysis but for operations that can easily be done in the standard library with a couple lines of code extra, numpy is not needed. why implement a third party lib unnecessarily?

# ? Oct 16, 2015 18:40

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# ? May 8, 2024 10:23

Symbolic Butt: Mar 22, 2009; (_!_); Buglord

I usually agree that numpy is overkill for most general stuff... But man, for this particular case array indexing fits like a glove as SurgicalOntologist showed.

So I would've posted this instead:

SurgicalOntologist posted:

You should be lusting for numpy.

# ? Oct 16, 2015 19:58

The Something Awful Forums > Discussion > Serious Hardware/Software Crap > The Cavern of COBOL > Python information and short questions megathread.

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