How to Fix Library Coredll.dll Required Via Ctypes Not Found Error in Python
Library Coredll.dll Required Via Ctypes Not Found
If you are a Python programmer who needs to call functions in dynamic link libraries (DLLs), you may have encountered the error message "library coredll.dll required via ctypes not found". This error can prevent you from loading and using the DLL file in your Python code, and cause frustration and confusion. In this article, we will explain what a DLL file is, what ctypes is, what causes this error, and how to fix it.
Library Coredll.dll Required Via Ctypes Not Found
What is a DLL file and what is ctypes?
A DLL file is a binary file that contains code and data that can be used by multiple programs at the same time. DLL files are commonly used to provide common functionality or features for different applications, such as user interface elements, database access, network communication, etc. By using DLL files, programs can reduce their size, improve their performance, and save memory and disk space.
ctypes is a Python module that allows you to create and manipulate C data types in Python, and to call functions in DLLs or shared libraries. It provides C compatible data types, such as integers, floats, strings, pointers, structures, etc., and allows you to wrap these libraries in pure Python. ctypes is useful for interfacing with low-level libraries or APIs that are written in C or other languages.
What is the problem of library coredll.dll required via ctypes not found?
The problem of library coredll.dll required via ctypes not found occurs when you try to load a DLL file using ctypes, but Python cannot find or load the DLL file. For example, if you have a DLL file named coredll.dll that contains some functions that you want to use in your Python code, you may write something like this:
from ctypes import * lib = cdll.coredll # try to load coredll.dll using cdll object
However, when you run this code, you may get an error message like this:
Traceback (most recent call last): File "", line 2, in
File "C:\Python39\lib\ctypes\__init__.py", line 452, in __getattr__ self._handle = _dlopen(self._name, mode) FileNotFoundError: Could not find module 'coredll.dll' (or one of its dependencies). Try using the full path with constructor syntax.
This means that Python cannot locate or access the coredll.dll file on your system. As a result, you cannot use the functions or data that are contained in the coredll.dll file.
What are the possible causes and solutions of the problem?Causes and solutions
There are several possible causes and solutions for the problem of library coredll.dll required via ctypes not found. Here are some of the most common ones:
Cause 1: The DLL file is missing or corrupted
One of the simplest reasons why Python cannot find or load the DLL file is that the DLL file is missing or corrupted on your system. This can happen due to accidental deletion, virus infection, disk failure, or other reasons.
Solution 1: Download and install the DLL file from a reliable source
If you know where the DLL file came from, you can try to download and install it again from a reliable source. For example, if the DLL file is part of a software package that you installed, you can try to reinstall or update the software. If the DLL file is from a third-party library that you downloaded, you can try to download it again from the official website or a trusted repository. Make sure that you download the correct version and architecture of the DLL file for your system.
Solution 2: Run a system file checker scan to repair the DLL file
If the DLL file is part of the Windows system files, you can try to run a system file checker scan to repair it. The system file checker is a built-in tool that scans and verifies the integrity of the system files and replaces any corrupted or missing files with a cached copy. To run a system file checker scan, follow these steps:
Open a command prompt as an administrator.
Type sfc /scannow and press Enter.
Wait for the scan to complete. It may take some time depending on the size and condition of your system files.
If the scan finds any problems, it will try to fix them automatically. You may need to restart your computer after the scan.
After running the system file checker scan, try to load the DLL file again using ctypes and see if the problem is resolved.
Cause 2: The DLL file has dependencies that are not met
Another possible reason why Python cannot find or load the DLL file is that the DLL file has dependencies that are not met. Dependencies are other DLL files or libraries that are required by the DLL file to function properly. If these dependencies are missing, outdated, or incompatible, the DLL file may fail to load.
Solution 1: Use a DLL dependency checker tool to identify and resolve the missing dependencies
One way to find out what dependencies are required by the DLL file is to use a DLL dependency checker tool. A DLL dependency checker tool is a program that analyzes a DLL file and lists all the other DLL files or libraries that it depends on. Some examples of DLL dependency checker tools are Dependency Walker, Dependencies, and PE Explorer. You can use any of these tools to open the coredll.dll file and see what dependencies it has.
Once you have identified the missing dependencies, you can try to download and install them from their respective sources. Make sure that you download the correct version and architecture of the dependencies for your system. You may also need to register them using regsvr32 or place them in the same folder as the coredll.dll file.
Solution 2: Use os.add_dll_directory or LoadLibraryEx to specify the DLL search path
Another way to resolve the missing dependencies is to use os.add_dll_directory or LoadLibraryEx to specify the DLL search path. The DLL search path is a list of directories where Python looks for DLL files when loading them using ctypes. By default, Python uses several directories as the DLL search path, such as sys.path, PYTHONPATH, PYTHONHOME, etc. However, sometimes these directories may not contain all the dependencies that are required by the coredll.dll file.
To add more directories to the DLL search path, you can use os.add_dll_directory, which is available in Python 3.8 and later. This function takes a directory as an argument and adds it to the beginning of the DLL search path. For example, if you have a directory named C:\mydlls that contains some dependencies for coredll.dll, you can write something like this:
from ctypes import * import os with os.add_dll_directory("C:\\mydlls"): # add C:\mydlls to the DLL search path lib = cdll.coredll # try to load coredll.dll using cdll object
This will make Python look for the dependencies in C:\mydlls before looking in other directories.
If you are using an older version of Python, you can use LoadLibraryEx instead of os.add_dll_directory. This function takes a DLL file name and a flag as arguments and loads the DLL file with the specified flag. The flag can be one of the following values:
FlagDescription
DONT_RESOLVE_DLL_REFERENCESDo not load the DLL's dependencies.
LOAD_LIBRARY_AS_DATAFILELoad the DLL as a data file, not as an executable file.
LOAD_LIBRARY_AS_DATAFILE_EXCLUSIVELoad the DLL as a data file, not as an executable file, and prevent other processes from writing to it.
LOAD_LIBRARY_AS_IMAGE_RESOURCELoad the DLL as an image resource, not as an executable file.
LOAD_LIBRARY_SEARCH_APPLICATION_DIRSearch for the DLL and its dependencies in the application directory.
LOAD_LIBRARY_SEARCH_DEFAULT_DIRSSearch for the DLL and its dependencies in the default directories.
LOAD_LIBRARY_SEARCH_DLL_LOAD_DIRSearch for the DLL and its dependencies in the directory that contains the DLL.
LOAD_LIBRARY_SEARCH_SYSTEM32Search for the DLL and its dependencies in the System32 directory.
LOAD_LIBRARY_SEARCH_USER_DIRSSearch for the DLL and its dependencies in the directories specified by AddDllDirectory.
LOAD_WITH_ALTERED_SEARCH_PATHUse an alternative search path for the DLL and its dependencies.
To use LoadLibraryEx, you need to import it from windll.kernel32, which is a ctypes object that represents the kernel32.dll file. For example, if you want to load coredll.dll with the flag LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR, you can write something like this:
from ctypes import * from ctypes.wintypes import * windll.kernel32.LoadLibraryExW.restype = HMODULE # set the return type to HMODULE windll.kernel32.LoadLibraryExW.argtypes = [LPCWSTR, HANDLE, DWORD] # set the argument types to LPCWSTR, HANDLE, and DWORD lib = windll.kernel32.LoadLibraryExW("coredll.dll", None, LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR) # load coredll.dll with the flag
This will make Python look for the dependencies in the directory that contains coredll.dll.
Cause 3: The DLL file is incompatible with the Python version or platform
A third possible reason why Python cannot find or load the DLL file is that the DLL file is incompatible with the Python version or platform. For example, if you are using a 64-bit Python interpreter, but the DLL file is compiled for 32-bit, or vice versa, you may encounter this problem. Similarly, if you are using a different version of Python than the one that the DLL file was built for, you may also face this issue.
Solution 1: Use a compatible DLL file for the Python version and platform
The best solution for this problem is to use a compatible DLL file for your Python version and platform. For example, if you are using a 64-bit Python interpreter, you should use a 64-bit DLL file. If you are using Python 3.9, you should use a DLL file that was built for Python 3.9. You can check your Python version and platform by running python --version and python -c "import platform; print(platform.architecture())" in a command prompt. You can also check the DLL file's version and platform by using a tool like PE Viewer or Resource Hacker.
Solution 2: Use a different Python module or library that does not require the DLL file
If you cannot find or use a compatible DLL file for your Python version and platform, you may consider using a different Python module or library that does not require the DLL file. For example, if you want to use coredll.dll for accessing the Windows API, you may try using the pywin32 module, which provides a Python interface to the Windows API. You can install pywin32 using pip install pywin32 or download it from [here]. You can then use the win32api module to call the Windows API functions. For example, if you want to use the GetSystemTime function from coredll.dll, you can write something like this:
import win32api st = win32api.GetSystemTime() # get the system time as a tuple print(st)
This will print something like this:
(2023, 6, 2, 13, 1, 2, 28, 0) # (year, month, dayOfWeek, day, hour, minute, second, millisecond)
By using a different Python module or library that does not require the DLL file, you can avoid the problem of library coredll.dll required via ctypes not found.
Conclusion
In this article, we have explained what a DLL file is, what ctypes is, what causes the problem of library coredll.dll required via ctypes not found, and how to fix it. We have discussed three possible causes and solutions for this problem: the DLL file is missing or corrupted, the DLL file has dependencies that are not met, and the DLL file is incompatible with the Python version or platform. We have also provided some code examples and tools to help you resolve this issue.
We hope that this article has helped you understand and solve the problem of library coredll.dll required via ctypes not found. If you have any feedback or questions, please feel free to leave a comment below. Thank you for reading!
FAQs
What is the difference between cdll, windll, and oledll in ctypes?
cdll, windll, and oledll are three ctypes objects that represent different types of DLL files. cdll represents a standard C calling convention DLL file, which passes arguments on the stack and returns values in registers. windll represents a Windows calling convention DLL file, which passes arguments on the stack and cleans up the stack after returning. oledll represents an OLE calling convention DLL file, which passes arguments in registers and returns values in an extra argument.
How can I specify the argument types and return types of a DLL function in ctypes?
You can specify the argument types and return types of a DLL function in ctypes by using the argtypes and restype attributes of the function object. For example, if you have a DLL function named Add that takes two integers as arguments and returns an integer as a result, you can write something like this:
from ctypes import * lib = cdll.mydll # load mydll.dll using cdll object lib.Add.argtypes = [c_int, c_int] # set the argument types to c_int lib.Add.restype = c_int # set the return type to c_int result = lib.Add(10, 20) # call Add with two integers print(result) # print the result
This will print something like this:
30 # the result of adding 10 and 20
How can I pass pointers or structures to a DLL function in ctypes?
You can pass pointers or structures to a DLL function in ctypes by using the byref, pointer, or POINTER functions. For example, if you have a DLL function named Multiply that takes two pointers to integers as arguments and modifies them by multiplying them by 10, you can write something like this:
from ctypes import * lib = cdll.mydll # load mydll.dll using cdll object a = c_int(5) # create a c_int object with value 5 b = c_int(10) # create another c_int object with value 10 lib.Multiply(byref(a), byref(b)) # call Multiply with pointers to a and b print(a.value) # print the value of a print(b.value) # print the value of b
This will print something like this:
50 # the value of a after multiplying by 10 100 # the value of b after multiplying by 10
How can I create a callback function in Python and pass it to a DLL function in ctypes?
You can create a callback function in Python and pass it to a DLL function in ctypes by using the CFUNCTYPE or WINFUNCTYPE functions. These functions create a callable object that wraps a Python function and makes it compatible with the C or Windows calling convention. For example, if you have a DLL function named Apply that takes an integer and a pointer to a function as arguments and applies the function to the integer, you can write something like this:
from ctypes import * lib = cdll.mydll # load mydll.dll using cdll object def square(x): # define a Python function that squares a number return x * x callback = CFUNCTYPE(c_int, c_int)(square) # create a callback object that wraps the square function result = lib.Apply(10, callback) # call Apply with 10 and the callback object print(result) # print the result
This will print something like this:
100 # the result of applying the square function to 10
How can I access values exported from a DLL in Python?
You can access values exported from a DLL in Python by using the in_dll function. This function takes a ctypes object that represents a DLL file and a string that represents the name of the exported value, and returns a ctypes object that represents the value. For example, if you have a DLL file named mydll.dll that exports a global variable named g_value of type int, you can write something like this:
from ctypes import * lib = cdll.mydll # load mydll.dll using cdll object g_value = c_int.in_dll(lib, "g_value") # get the g_value object from the DLL file print(g_value.value) # print the value of g_value
This will print something like this:
42 # the value of g_value dcd2dc6462