make image, weight etc. refs of observations read only by default about ngmix HOT 2 CLOSED

import numpy as np


class C(object):
    def __init__(self):
        self._data = np.zeros(5)
        self._writeable = False

    @property
    def data(self):
        dview = self._data.view()
        dview.flags['WRITEABLE'] = self._writeable
        return dview

    def writeable(self):
        self._writeable = True
        return self

    def __enter__(self):
        return self

    def __exit__(self, exception_type, exception_value, traceback):
        self._writeable = False


c = C()
print(c.data)

try:
    c.data[1] = 5
except ValueError as err:
    print("as expected raised error '%s'" % err)


with c.writeable():
    c.data[1] = 5

print(c.data)

try:
    c.data[1] = 5
except ValueError as err:
    print("as expected raised error '%s'" % err)

import numpy as np


class C(object):
    def __init__(self):
        self._data = np.zeros(5)
        self.update_pixels()
        self._writeable = False

    def update_pixels(self):
        self._pixels = self._data.copy()

    @property
    def data(self):
        return self._get_view(self._data)

    @property
    def pixels(self):
        return self._get_view(self._pixels)

    def _get_view(self, data):
        view = data.view()
        view.flags['WRITEABLE'] = self._writeable
        return view

    def writeable(self):
        return self

    def __enter__(self):
        self._writeable = True
        return self

    def __exit__(self, exception_type, exception_value, traceback):
        self._writeable = False
        self.update_pixels()


c = C()

try:
    c.data[1] = 5
except ValueError as err:
    print("as expected raised error '%s'" % err)

assert c.data[1] == 0.0
assert c.pixels[1] == 0.0

with c.writeable():
    c.data[1] = 5

assert c.data[1] == 5
assert c.pixels[1] == 5

try:
    c.data[1] = 25
except ValueError as err:
    print("as expected raised error '%s'" % err)

assert c.data[1] == 5
assert c.pixels[1] == 5