For the example above, we can read in the docs that Microsoft provides that GetSystemMetrics is a method that accepts one parameter, an integer representing an index of system information to retrieve:. The docs also specify how an integer parameter maps to a system metric.
Based on this information, we put together than we can call User GetSystemMetrics 1 to get the height of the primary monitor. Sometimes we're not fortunate enough to know ahead of time or have references available to us. They're also not super convenient even when you have them, either.
You'll notice that, unlike a lot of ordinary Python classes, the User32 object we made before doesn't tell us what methods exist in the DLL. You can try calling dir User32 but that won't yield you any useful information. If you went to venture on how to get this information without docs, you'd probably be told to use a DLL exporter or COM browser. Enter pywin Among its many features is the win32com. You can install pywin32 using pip python -m pip install pywin But the really interesting part is being able to generate Python classes for the COM interfaces automagically.
To get started generating a Python file you can run this command from a shell. If you don't give it an input of what library you want to generate, it will prompt you to choose one. So you could even do things like help faxcomex.
Connect in an interactive shell. Pretty neat! If you're so inclined, you could even copy that generated code to something like faxcomex. You are commenting using your Twitter account. You are commenting using your Facebook account. Notify me of new comments via email. Notify me of new posts via email. This site uses Akismet to reduce spam.
Learn how your comment data is processed. Skip to content Python comes with a bunch of standard modules. To view all your installed libraries, enter: pip list You can list your outdated packages with the —outdated argument: pip list --outdated Supplementary Resources I recommend taking a look at this list of 20 modules to get started. Here is another more comprehensive list of libraries you can now install.
PyPI, the Python Package Index is the primary repository that houses a variety of libraries that are typically downloadable by pip. Swing by the pip documentation Quickstart and User Guide to learn some helpful commands. I also like this pip cheat sheet from opensource. Congrats on figuring out how to install packages with pip, have fun!
Try using the ensurepip command. This command will install and upgrade pip to the newest version. New in Python 3. Share this: Twitter Facebook. Tom Hennen Tom Hennen 4, 7 7 gold badges 32 32 silver badges 43 43 bronze badges. Remuze did you tag the wrong question or tag with the wrong answer?
They're both python, but I see no reason why you'd find them at all similar and I checked the revision history to make sure it wasn't somehow closer at some point in the past — Foon. Add a comment. Active Oldest Votes. Set up the variables and call the Python name with them. Hello, it may be a long time since someone replied here but I wanted to know something to make this work exactly for my program. What exactly does hllApiParams do? What is the point of those tuples?
It's hard to match up some of the things in this example with the documentation. JonathonReinhart, I've fleshed out the specific example a bit with some text at the bottom. Hopefully, that explains it a little better. If not, let me know and I'll try again :- — paxdiablo. This is super confusing from a ctypes newcomers perspective.. Not exactly sure what is going on, even with the explanation.
Show 9 more comments. Community Bot 1 1 1 silver badge. The link in this answer is broken. If the link doesn't work for you do not worry, it is a direct copy paste. You are not missing any info. Building a DLL and linking it under Python using ctypes I present a fully worked example on how building a shared library and using it under Python by means of ctypes. LoadLibrary 'testDLL. You can also use a callable Python object a function or a class for example as the restype attribute, if the foreign function returns an integer.
The callable will be called with the integer the C function returns, and the result of this call will be used as the result of your function call. This is useful to check for error return values and automatically raise an exception:. WinError is a function which will call Windows FormatMessage api to get the string representation of an error code, and returns an exception.
WinError takes an optional error code parameter, if no one is used, it calls GetLastError to retrieve it. Please note that a much more powerful error checking mechanism is available through the errcheck attribute; see the reference manual for details. Sometimes a C api function expects a pointer to a data type as parameter, probably to write into the corresponding location, or if the data is too large to be passed by value.
This is also known as passing parameters by reference. Structures and unions must derive from the Structure and Union base classes which are defined in the ctypes module. Here is a simple example of a POINT structure, which contains two integers named x and y , and also shows how to initialize a structure in the constructor:.
You can, however, build much more complicated structures. A structure can itself contain other structures by using a structure as a field type.
Field descriptor s can be retrieved from the class , they are useful for debugging because they can provide useful information:. Unions and structures with bit-fields should always be passed to functions by pointer. By default, Structure and Union fields are aligned in the same way the C compiler does it.
This must be set to a positive integer and specifies the maximum alignment for the fields. This is what pragma pack n also does in MSVC. These classes cannot contain pointer fields. It is possible to create structures and unions containing bit fields. Here is an example of a somewhat artificial data type, a structure containing 4 POINTs among other stuff:.
The above code print a series of 0 0 lines, because the array contents is initialized to zeros. Pointer instances are created by calling the pointer function on a ctypes type:. Pointer instances have a contents attribute which returns the object to which the pointer points, the i object above:.
Note that ctypes does not have OOR original object return , it constructs a new, equivalent object each time you retrieve an attribute:. Generally you only use this feature if you receive a pointer from a C function, and you know that the pointer actually points to an array instead of a single item.
Behind the scenes, the pointer function does more than simply create pointer instances, it has to create pointer types first. Calling the pointer type without an argument creates a NULL pointer. NULL pointers have a False boolean value:. Usually, ctypes does strict type checking. There are some exceptions to this rule, where ctypes accepts other objects.
For example, you can pass compatible array instances instead of pointer types. Sometimes you have instances of incompatible types. In C, you can cast one type into another type.
For these cases, the cast function is handy. The cast function can be used to cast a ctypes instance into a pointer to a different ctypes data type. It returns an instance of the second argument, which references the same memory block as the first argument:. So, cast can be used to assign to the values field of Bar the structure:.
Incomplete Types are structures, unions or arrays whose members are not yet specified. In C, they are specified by forward declarations, which are defined later:.
We create two instances of cell , and let them point to each other, and finally follow the pointer chain a few times:. These are sometimes called callback functions. First, you must create a class for the callback function. The class knows the calling convention, the return type, and the number and types of arguments this function will receive. Both of these factory functions are called with the result type as first argument, and the callback functions expected argument types as the remaining arguments.
The callback will then be called with two pointers to items, and it must return a negative integer if the first item is smaller than the second, a zero if they are equal, and a positive integer otherwise. So our callback function receives pointers to integers, and must return an integer.
First we create the type for the callback function:. This behavior is correct for most purposes, but it means that values stored with threading. Some shared libraries not only export functions, they also export variables. When a frozen module is imported, it is searched in this table. Third-party code could play tricks with this to provide a dynamically created collection of frozen modules. So manipulating this pointer could even prove useful. To restrict the example size, we show only how this table can be read with ctypes :.
The fact that standard Python has a frozen module and a frozen package indicated by the negative size member is not well known, it is only used for testing.
There are some edges in ctypes where you might expect something other than what actually happens. We certainly expected the last statement to print 3 4 1 2. What happened? Here are the steps of the rc. Note that temp0 and temp1 are objects still using the internal buffer of the rc object above. So executing rc. This, in turn, changes the contents of temp1. So, the last assignment rc. Why is it printing False?
Storing a Python object in the memory block does not store the object itself, instead the contents of the object is stored. Accessing the contents again constructs a new Python object each time!
The resize function can be used to resize the memory buffer of an existing ctypes object. The function takes the object as first argument, and the requested size in bytes as the second argument. The memory block cannot be made smaller than the natural memory block specified by the objects type, a ValueError is raised if this is tried:.
This is nice and fine, but how would one access the additional elements contained in this array? Since the type still only knows about 4 elements, we get errors accessing other elements:. Another way to use variable-sized data types with ctypes is to use the dynamic nature of Python, and re- define the data type after the required size is already known, on a case by case basis.
The ctypes. Try to find a library and return a pathname. If no library can be found, returns None. It returns the filename of the library file. There are several ways to load shared libraries into the Python process.
One way is to instantiate one of the following classes:. Instances of this class represent loaded shared libraries. Functions in these libraries use the standard C calling convention, and are assumed to return int. This error message does not contain the name of the missing DLL because the Windows API does not return this information making this error hard to diagnose.
To resolve this error and determine which DLL is not found, you need to find the list of dependent DLLs and determine which one is not found using Windows debugging and tracing tools. Windows only: Instances of this class represent loaded shared libraries, functions in these libraries use the stdcall calling convention, and are assumed to return the windows specific HRESULT code.
HRESULT values contain information specifying whether the function call failed or succeeded, together with additional error code. If the return value signals a failure, an OSError is automatically raised. Windows only: Instances of this class represent loaded shared libraries, functions in these libraries use the stdcall calling convention, and are assumed to return int by default.
The Python global interpreter lock is released before calling any function exported by these libraries, and reacquired afterwards.
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