gphoto2 0.9.1

Install with pip

The easiest installation method is to use the pip command:

sudo pip install gphoto2

Install with git

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

Install a downloaded archive

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

Testing

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.

“C” interface

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: Context *


    See also: gphoto2.Camera.folder_list_files

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)

“Object oriented” interface

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 are some functions in the “C” interface that do not have corresponding member methods. Those that do include a “see also” reference in their docstring, as shown in the pydoc example above.

Error checking

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
...