The result is cached, so repeated attribute accesses return the same library each time. Load a shared library into the process and return it. This method always returns a new instance of the library. Creates CDLL instances. Creates PyDLL instances. For accessing the C Python api directly, a ready-to-use Python shared library object is available:.
Note that all these functions are assumed to return C int , which is of course not always the truth, so you have to assign the correct restype attribute to use these functions. Loading a library through any of these objects raises an auditing event ctypes. Accessing a function on a loaded library raises an auditing event ctypes. In cases when only the library handle is available rather than the object, accessing a function raises an auditing event ctypes.
As explained in the previous section, foreign functions can be accessed as attributes of loaded shared libraries. The function objects created in this way by default accept any number of arguments, accept any ctypes data instances as arguments, and return the default result type specified by the library loader. They are instances of a private class:. Instances of foreign functions are also C compatible data types; they represent C function pointers.
This behavior can be customized by assigning to special attributes of the foreign function object. Assign a ctypes type to specify the result type of the foreign function. Use None for void , a function not returning anything. It is possible to assign a callable Python object that is not a ctypes type, in this case the function is assumed to return a C int , and the callable will be called with this integer, allowing further processing or error checking.
Using this is deprecated, for more flexible post processing or error checking use a ctypes data type as restype and assign a callable to the errcheck attribute. Assign a tuple of ctypes types to specify the argument types that the function accepts.
Functions using the stdcall calling convention can only be called with the same number of arguments as the length of this tuple; functions using the C calling convention accept additional, unspecified arguments as well. This allows defining adapters that can adapt custom objects as function parameters.
Assign a Python function or another callable to this attribute. The callable will be called with three or more arguments:. The object that this function returns will be returned from the foreign function call, but it can also check the result value and raise an exception if the foreign function call failed. This exception is raised when a foreign function call cannot convert one of the passed arguments. On Windows, when a foreign function call raises a system exception for example, due to an access violation , it will be captured and replaced with a suitable Python exception.
Further, an auditing event ctypes. Some ways to invoke foreign function calls may raise an auditing event ctypes. Foreign functions can also be created by instantiating function prototypes.
Function prototypes are similar to function prototypes in C; they describe a function return type, argument types, calling convention without defining an implementation.
The factory functions must be called with the desired result type and the argument types of the function, and can be used as decorator factories, and as such, be applied to functions through the wrapper syntax.
See Callback functions for examples. The returned function prototype creates functions that use the standard C calling convention. The function will release the GIL during the call. The returned function prototype creates functions that use the Python calling convention. The function will not release the GIL during the call. Function prototypes created by these factory functions can be instantiated in different ways, depending on the type and number of the parameters in the call:.
Returns a foreign function exported by a shared library. The first item is the name of the exported function as string, or the ordinal of the exported function as small integer. The second item is the shared library instance. Returns a foreign function that will call a COM method. COM methods use a special calling convention: They require a pointer to the COM interface as first argument, in addition to those parameters that are specified in the argtypes tuple.
The optional paramflags parameter creates foreign function wrappers with much more functionality than the features described above. Each item in this tuple contains further information about a parameter, it must be a tuple containing one, two, or three items. The optional second item is the parameter name as string.
If this is specified, the foreign function can be called with named parameters. This example demonstrates how to wrap the Windows MessageBoxW function so that it supports default parameters and named arguments. The C declaration from the windows header file is this:.
Here is the wrapping with ctypes :. The MessageBox foreign function can now be called in these ways:. A second example demonstrates output parameters. The win32 GetWindowRect function retrieves the dimensions of a specified window by copying them into RECT structure that the caller has to supply. Here is the C declaration:. Functions with output parameters will automatically return the output parameter value if there is a single one, or a tuple containing the output parameter values when there are more than one, so the GetWindowRect function now returns a RECT instance, when called.
Output parameters can be combined with the errcheck protocol to do further output processing and error checking.
The win32 GetWindowRect api function returns a BOOL to signal success or failure, so this function could do the error checking, and raises an exception when the api call failed:. If the errcheck function returns the argument tuple it receives unchanged, ctypes continues the normal processing it does on the output parameters.
If you want to return a tuple of window coordinates instead of a RECT instance, you can retrieve the fields in the function and return them instead, the normal processing will no longer take place:.
Returns the address of the memory buffer as integer. Raises an auditing event ctypes. Returns the alignment requirements of a ctypes type. Returns a light-weight pointer to obj , which must be an instance of a ctypes type. The returned object can only be used as a foreign function call parameter. It behaves similar to pointer obj , but the construction is a lot faster. This function is similar to the cast operator in C. It returns a new instance of type which points to the same memory block as obj.
This function creates a mutable character buffer. If a bytes object is specified as first argument, the buffer is made one item larger than its length so that the last element in the array is a NUL termination character. An integer can be passed as second argument which allows specifying the size of the array if the length of the bytes should not be used.
This function creates a mutable unicode character buffer. If a string is specified as first argument, the buffer is made one item larger than the length of the string so that the last element in the array is a NUL termination character.
An integer can be passed as second argument which allows specifying the size of the array if the length of the string should not be used. Windows only: This function is a hook which allows implementing in-process COM servers with ctypes. Windows only: return the filename of the VC runtime library used by Python, and by the extension modules.
If the name of the library cannot be determined, None is returned. Windows only: Returns a textual description of the error code code. If no error code is specified, the last error code is used by calling the Windows api function GetLastError.
Windows only: Returns the last error code set by Windows in the calling thread. This function calls the Windows GetLastError function directly, it does not return the ctypes-private copy of the error code.
Returns the current value of the ctypes-private copy of the system errno variable in the calling thread. Windows only: returns the current value of the ctypes-private copy of the system LastError variable in the calling thread.
Same as the standard C memmove library function: copies count bytes from src to dst. Same as the standard C memset library function: fills the memory block at address dst with count bytes of value c. This factory function creates and returns a new ctypes pointer type. Pointer types are cached and reused internally, so calling this function repeatedly is cheap.
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.
The same effect can be achieved with the pointer function, although pointer does a lot more work since it constructs a real pointer object, so it is faster to use byref if you don't need the pointer object in Python itself:.
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. Structures can itself contain other structures by using a structure as a field type. Fields descriptors can be retrieved from the class , they are useful for debugging because they can provide useful information:.
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 an somewhat artifical 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:. It is also possible to use indexes different from 0, but you must know what you're doing, just as in C: You can access or change arbitrary memory locations.
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. An interpreter executes a program, interpreting each statement into a sequence of one or more subroutines and then into machine code.
Python and JavaScript are common examples of interpreted languages. Say you just want to write a small utility or a patch for some application. Python, on the contrary, has convenient tools like pip and virtual environments for handling dependencies. Also, it allows for fast development, has various useful third-party libraries, and offers convenient environment configuration.
Python is one of the most popular interactive programming languages. Its biggest advantage is its simple syntax that allows you to write programs with less code than other programming languages require.
And since its syntax is highly readable and similar to English, all team members can easily understand it. You can execute Python code right after it's written. However, since Python is an interpreted language, it requires an executor — an interpreter called the Python virtual machine. As we wrote in our previous article , to hook API functions, the hooking code should be injected inside the memory address space of the target process.
If our hooking code is written in Python, the target process should be able to execute it. But the target application may not know about Python, its virtual machine, or any interpreted language at all.
To make Python code run inside the target application, you may need to inject a Python virtual machine into it. To make the Python virtual machine run in the target process, you only need to perform a few steps:. Now, we will load the phyton.
The target process can now execute any Python code. We can see that python. This structure contains library names used by a certain application. For each library, the IAT also contains a list of features imported from this library.
Thus, when launching an application, a loader can know what libraries to load and how to connect function addresses from these libraries. The IAT contains pointers to information that is critical for an executable to do its job:. Every imported module has a list of functions imported from it by the current process. However, hooking API functions in Python also requires using various libraries. In the previous section, we discussed that dynamic languages may not be the best choice for such low-level development tasks as injecting code and modifying import tables because all internal structures should be defined almost from scratch.
However, Python has lots of useful third-party libraries that can significantly simplify various development tasks. In this section, we explore two Python libraries that can ease the process of WinAPI function hooking.
Deviare is a professional open-source hooking library for instrumenting arbitrary Win32 functions, COM objects, and functions whose symbols are located in program databases PDBs. Connect and share knowledge within a single location that is structured and easy to search. I've looked at the example given here ctypes - Beginner and followed the same steps with a different bit of C code.
I've built a. The dll and the. Can anyone help me understand what's going on here. I've spent hours trying to figure this out, but have hit a wall. Make sure your compiler and version of Python are both bit or both bit. That's the cause of the name mangling mention in your answer. After further digging I've found out the solution. The C compiler has mangled the name of the function which is why I got an Attribute error when calling the sum method.
I had to use link. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow.
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