I was playing around with the location module the other day and was wondering about how it deals with scripts closing without manually turning off location tracking. So I made a context Manager for the location module

import location


class LocationManager (object):
    def __enter__(self):
        location.start_updates()

    def __exit__(self):
        location.stop_updates()

You can use it like so:

with LocationManager():
    # Do stuff that requires `location` here...
    ...

Now, this may be completely unnecessary, but I have found it useful for applications where constant location updates are not needed (e.g. get my location every 15 minutes or set my initial location for some one off script).

@omz also think this may be a good feature for the built-in location module to adopt (if possible). So we can have both location.start(stop)_updates() or with location: ....

Let me know what y'all think (criticism is welcome).

B.

EDIT
A bit less verbose code with the help of @ccc on contexlib

import contexlib
import location

@contexlib.contexmanager
def location_enabled():
    location.start_updates()
    yield
    location.stop_updates()

the use case is still the same.

with location_enabled():
    # Do location stuff here...
    ...

@bistrot Add the #! python2 she-bang at the top of the script to tell it to use the (possibly) nom-default python 2.7 interpreter.

@omz and @Cethric thanks for the help. It seems to work.

I have a script where I'm trying to get the system attributes; eventually this will gather memory information. I have isolated the crash to this line of code:

from ctypes import POINTER
from objc_util import ObjCClass, ObjCInstance, c, c_void_p


NSHomeDirectory = c.NSHomeDirectory
NSHomeDirectory.restype = c_void_p
NSHomeDirectory.argtype = []

NSFileManager = ObjCClass('NSFileManager')

LP_c_void_p = POINTER(c_void_p)

def get_system_attributes():
    file_manager = NSFileManager.defaultManager()
    error = LP_c_void_p()
    attributes = file_manager.attributesOfFileSystemForPath_error_(
        ObjCInstance(
            NSHomeDirectory()
        ).cString(),
        error
    )
    return attributes

get_system_attributes()

attributesOfFileSystemForPath_error_ takes a string and an error pointer. It crashes when it gets to the error inside that function. I think it crashes due to an NSError object being created. Any ideas on how to stop the crash?

@Phuket2 quoted from the Apple developer forums:

Retina Flash
iPhone 6s and 6s Plus contain a custom display chip that allows the retina display to briefly flash 3 times brighter than its usual maximum illuminance. No new API was added to support this feature. Since iOS 4, AVCaptureDevice has supported the -hasFlash, -isFlashModeSupported: and -flashMode properties. The iPhone 6s and 6s Plus front-facing cameras are the first front-facing iOS cameras to respond YES to the -hasFlash property. By setting the front-facing camera's flashMode to AVCaptureFlashModeOn or AVCaptureFlashModeAuto, the retina flash fires when a still image is captured (see AVCaptureStillImageOutput’s captureStillImageAsynchronouslyFromConnection:completionHandler:), just as the True Tone flash fires for rear-facing camera stills.

Hope this. Only works on 6s, 6s+, and SE.
B.

@Tizzy sorry for not explaining myself better. @dgelessus is correct about the ? being the important part.

I checked MySQL and it has its own syntax for variable arguments that just so happens to be %s. Shame on them…

@Tizzy it is good practice to not do statement = 'SELECT * FROM ' + table_name' or even statement = 'SELECT * FROM ' + %s' % table_name as this can cause security issues with SQL injection. Most database packages (read: modules) will have something along the lines of

statement = '''
SELECT *
FROM ?
'''
with db.connect as conn:
    result = conn.execute(statement, (table_name,))

This is a more secure way of accessing batabases. The other way is good enough for person projects, but keep that in mind or little Bobby Tables will make your life awful as a DBA.

B.

@omz said:

Btw, you can just pass a prefix to ObjCClass.get_names() instead of doing the filtering yourself (in the current beta, it would have to be a byte string though).

Did not know that…

Hey @omz, I got back in to playing around with objc_util and found this:

>>> dir(OMJavaScriptSyntaxHighlighter)
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/var/mobile/Containers/Bundle/Application/61407674-7331-47C2-B308-BDB7BBE52166/Pythonista3.app/Frameworks/PythonistaKit3.framework/pylib/site-packages/objc_util.py", line 380, in __dir__
    py_method_name = sel_name.replace(':', '_')
TypeError: a bytes-like object is required, not 'str'

This error come from the way Python3.* encodes ASCII vs Unicode strings. When you run the following:

om_classes = [cls for cls in ObjCClass.get_names() if cls.startswith(b'OM')]
for cls in om_classes:
    print(cls)

You get the following (truncated for brevity):

b'OMAutoresizingMaskView'
b'OMBarButton'
b'OMBarButtonItem'
b'OMBaseSyntaxHighlighter'
b'OMBasicPythonCompletionProvider'
b'OMBasicPythonCompletionProviderTokenizedLine'
b'OMButtonFieldSpecifier'
b'OMCSSSyntaxHighlighter'
b'OMCaretView'
b'OMCheckCell'
b'OMCheckFieldSpecifier'
…
b'OMUIWidgetViewScrollView'
b'OMUIWidgetViewSegmentedControl'
b'OMUIWidgetViewSlider'
b'OMUIWidgetViewStickyNote'
b'OMUIWidgetViewSwitch'
b'OMUIWidgetViewTableView'
b'OMUIWidgetViewTextField'
b'OMUIWidgetViewTextView'
b'OMUIWidgetViewWebView'

Notice the b before the string. So, when you want to run string operations, which are now encoded as UTF-8, it throws a TypeError because ASCII is (for whatever reason) a byte-like object, not a string.

To fix this you can have .get_names() return strings, or add the b prefix to the strings in replace() method in objc_util.

Noticed some bugs in the above code, so here are my fixes to make it work (in Pythonista3, at least).

# coding: utf-8

import ui
from objc_util import *

class BlurView (ui.View):
    def __init__(self, style=1, *args, **kwargs):
        ui.View.__init__(self, **kwargs)
        self._style = style
        self.effect_view = None
        self.setup_effect_view()
    
    @on_main_thread
    def setup_effect_view(self):
        if self.effect_view is not None:
            self.effect_view.removeFromSuperview()
        UIVisualEffectView = ObjCClass('UIVisualEffectView')
        UIVibrancyEffect = ObjCClass('UIVibrancyEffect')
        UIBlurEffect = ObjCClass('UIBlurEffect')
        UILabel = ObjCClass('UILabel')
        # Brooks patch for Rect not having a 'slice' 
        bounds = self.bounds.as_tuple()
        frame = (bounds[:2], bounds[2:])
        self.effect_view = UIVisualEffectView.alloc().initWithFrame_(frame).autorelease()
        effect = UIBlurEffect.effectWithStyle_(self._style)
        self.effect_view.effect = effect
        self.effect_view.setAutoresizingMask_(18)
        ObjCInstance(self).addSubview_(self.effect_view)
        vibrancy_effect = UIVibrancyEffect.effectForBlurEffect_(effect)
        self.vibrancy_view = UIVisualEffectView.alloc().initWithFrame_(frame).autorelease()
        self.vibrancy_view.effect = vibrancy_effect
        self.effect_view.contentView().addSubview_(self.vibrancy_view)
        
    @property
    def style(self):
        return self._style
    
    @style.setter
    def style(self, value):
        if value != self._style:
            self._style = value
            self.setup_effect_view()
    
    # Brooks fix @on_mains_thread to @on_main_thread
    @on_main_thread
    def add_vibrant_label(self, label):
        self.vibrancy_view.contentView().addSubview_(ObjCInstance(label))

def main():
    image_view = ui.ImageView(frame=(0, 0, 320, 320))
    image_view.image = ui.Image.named('test:Mandrill')
    blur_view = BlurView(style=2, frame=image_view.bounds.inset(40, 40))
    image_view.add_subview(blur_view)
    label = ui.Label(frame=blur_view.bounds)
    label.text = 'Hello World'
    label.font = ('HelveticaNeue', 40)
    label.alignment = ui.ALIGN_CENTER
    blur_view.add_vibrant_label(label)
    image_view.present('sheet')

main()

The biggest problem was that the ui.Rect() object does not have the ability to use slices. This was fixed with the ui.Rect().as_tuple() function. The second problem was just a typo.

B