python-gphoto2 is a comprehensive Python interface (or binding) to libgphoto2. It is built using SWIG to automatically generate the interface code. This gives direct access to nearly all the libgphoto2 functions, but sometimes in a rather un-Pythonic manner.
Other Python bindings to libgphoto2 are available. piggyphoto uses ctypes (included in standard Python installations) to interface to the library. The gphoto2 source tree includes some Python bindings which also use ctypes.
- Python: http://python.org/ version 2.6 or greater (including Python 3)
- SWIG: http://swig.org/ version 2.0 or higher
- libgphoto2: http://www.gphoto.org/proj/libgphoto2/ version 2.4 or greater
Note that you need the "development headers" versions of libgphoto2 and Python. Most Linux distributions' package managers have these, but the names vary. Look for libgphoto2-2-dev
or libgphoto2-devel
or something similar.
There are several ways to install python-gphoto2, with varying levels of control over the installation process. Note that they all need SWIG and the other dependencies - there are no "binary" packages at present.
The easiest installation method is to use the pip command:
sudo pip install gphoto2
To install the very latest version, use git to "clone" the GitHub repository, then change to the new directory:
git clone https://github.com/jim-easterbrook/python-gphoto2.git
cd python-gphoto2
Python's distutils are used to build and install python-gphoto2:
python setup.py build
sudo python setup.py install
Visit the project releases page or PyPI and download one of the zip or tar.gz files, then extract it and change to the new directory. For example:
tar xf python-gphoto2-gphoto2-0.9.0.tar.gz
cd python-gphoto2-gphoto2-0.9.0
As before, Python's distutils
are used to build and install python-gphoto2:
python setup.py build
sudo python setup.py install
Note
If you installed with pip the example files should be in /usr/share/python-gphoto2/examples
or /usr/local/share/python-gphoto2/examples
or somewhere similar (except for versions before 0.3.2, which didn't install the examples at all).
Connect a digital camera to your computer, switch it on, and try one of the example programs:
python examples/camera-summary.py
If this works then you're ready to start using python-gphoto2.
The Python interface to libgphoto2 should allow you to do anything you could do in a C program. However, the project is quite young and there are still bits missing and functions that cannot be called from Python. Let me know if you run into any problems.
The following paragraphs show how the Python interfaces differ from C. See the example programs for typical usage of the Python gphoto2 API.
Using SWIG to generate the Python interfaces automatically means that every function in libgphoto2 should be available to Python. The pydoc
command can be used to show basic information about a function:
jim@firefly ~/python-gphoto2 $ pydoc gphoto2.gp_camera_folder_list_files
Help on built-in function gp_camera_folder_list_files in gphoto2:
gphoto2.gp_camera_folder_list_files = gp_camera_folder_list_files(...)
gp_camera_folder_list_files(camera, folder, context) -> int
Parameters:
camera: Camera *
folder: char const *
context: GPContext *
jim@firefly ~/python-gphoto2 $
In general it is easier to use the C API documentation, but make sure you find the documentation for the version of libgphoto2 installed on your computer.
Note that there is one major difference between the Python and C APIs. C functions that use a pointer parameter to return a value (and often do some memory allocation) such as gp_camera_new() have Python equivalents that create the required pointer and return it in a list with the gphoto2 error code.
For example, the C code:
#include "gphoto2.h"
int error;
Camera *camera;
error = gp_camera_new(&camera);
...
error = gp_camera_unref(camera);
has this Python equivalent:
import gphoto2 as gp
error, camera = gp.gp_camera_new()
...
Note that the gp_camera_unref() call is not needed (since version 0.5.0). It is called automatically when the python camera object is deleted.
This conversion of "output" parameters is why the CameraList *list
parameter is not listed in the pydoc
example above but is shown in the C documentation. In Python a new CameraList
object is created and appended to the return value list. Unfortunately I've not found a way to persuade SWIG to include this extra return value in the documentation.
Here is a complete example program (without any error checking):
import gphoto2 as gp
context = gp.gp_context_new()
error, camera = gp.gp_camera_new()
error = gp.gp_camera_init(camera, context)
error, text = gp.gp_camera_get_summary(camera, context)
print('Summary')
print('=======')
print(text.text)
error = gp.gp_camera_exit(camera, context)
SWIG has the ability to attach member functions to C structs such as the GPhoto2 Camera
object. The Python interface includes many such member functions, allowing GPhoto2 to be used in a more "Pythonic" style. These member functions also include error checking. If an error occurs they raise a Python GPhoto2Error
exception.
The example program can be re-written as follows:
import gphoto2 as gp
context = gp.Context()
camera = gp.Camera()
camera.init(context)
text = camera.get_summary(context)
print('Summary')
print('=======')
print(str(text))
camera.exit(context)
The member functions are more "hand crafted" than the rest of the Python bindings, which are mostly automatically generated from the library header files. This means that there may be some functions in the "C" interface that do not have corresponding member methods.
Most of the libgphoto2 "C" functions return an integer to indicate success or failure. The Python interface includes a check_result()
function to check these values and raise a GPhoto2Error
exception if an error occurs.
This function also unwraps lists such as that returned by gp_camera_new()
in the example. Using this function the earlier example becomes:
import gphoto2 as gp
context = gp.gp_context_new()
camera = gp.check_result(gp.gp_camera_new())
gp.check_result(gp.gp_camera_init(camera, context))
text = gp.check_result(gp.gp_camera_get_summary(camera, context))
print('Summary')
print('=======')
print(text.text)
gp.check_result(gp.gp_camera_exit(camera, context))
There may be some circumstances where you don't want an exception to be raised when some errors occur. You can "fine tune" the behaviour of the check_result()
function by adjusting the error_severity
variable:
import gphoto2 as gp
gp.error_severity[gp.GP_ERROR] = logging.WARNING
...
In this case a warning message will be logged (using Python's standard logging module) but no exception will be raised when a GP_ERROR
error occurs. However, this is a "blanket" approach that treats all GP_ERROR
errors the same. It is better to test for particular error conditions after particular operations, as described below.
The GPhoto2Error
exception object has two attributes that may be useful in an exception handler. GPhoto2Error.code
stores the integer error generated by the library function and GPhoto2Error.string
stores the corresponding error message.
For example, to wait for a user to connect a camera you could do something like this:
import gphoto2 as gp
...
print('Please connect and switch on your camera')
while True:
try:
camera.init(context)
except gp.GPhoto2Error as ex:
if ex.code == gp.GP_ERROR_MODEL_NOT_FOUND:
# no camera, try again in 2 seconds
time.sleep(2)
continue
# some other error we can't handle here
raise
# operation completed successfully so exit loop
break
# continue with rest of program
...
When just calling a single function like this, it's probably easier to test the error value directly instead of using Python exceptions:
import gphoto2 as gp
...
print('Please connect and switch on your camera')
while True:
error = gp.gp_camera_init(camera, context)
if error >= gp.GP_OK:
# operation completed successfully so exit loop
break
if error != gp.GP_ERROR_MODEL_NOT_FOUND:
# some other error we can't handle here
raise gp.GPhoto2Error(error)
# no camera, try again in 2 seconds
time.sleep(2)
# continue with rest of program
...
python-gphoto2 - Python interface to libgphoto2 http://github.com/jim-easterbrook/python-gphoto2 Copyright (C) 2014 Jim Easterbrook jim@jim-easterbrook.me.uk
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.