What is Python sys Module?
→ Sys module in Python basically provides access to some variables used or maintained by the interpreter and some functions that interact strongly with the interpreter.
→ It is always available in the code library.
→ sys.modules return the name of the Python modules that the current shell has imported.
→ It provides information about constants, functions, and methods of the interpreter. But another possibility is the help() function.
→ Using help(sys) provides valuable detailed information about the interpreter and function.
Input and Output using sys:
→This module provides variable for better control over input and output.
→They using 3 variable in sys module are stdin, stdout, stderr.
stdin:
→ It is nothing but to get a input from command line directly.
→ It internally calls the input() method.
stdout:
→ It is used to display output directly to the screen console. Whenever a print function is called within the code, it is first written and then finally on the screen.
syntax: sys.stdout
stderr:
→ Whenever an exception occurs in Python it is written.
Syntax: sys.stderr
Basic Code of sys() in Python
Command Line Argument :
→ Command-line arguments are those which are passed the calling of the program along with the calling statement.
→ Sys module provides a variable called sys.argv.
It’s main purpose are:
- It is a list of command-line arguments.
- len(sys.argv) provides the number of command-line arguments.
- sys.argv[0] is the name of the current Python script.
Exiting the Program :
→ This causes the program to exit in a runtime freeing the space occupied.
→ sys.exit([arg]) can be used to exit the program.
Reference Count:
→ sys.getrefcount() is used to get the reference count for any given object.
→ When this value becomes 0, the memory for that particular value is deleted.
Working with Modules:
→ sys.path is a built-in variable within the sys module. Its returns the list of directories that the interpreter will search for the required module.
→ sys.setrecursionlimit() method is used to set the maximum depth of the Python interpreter stack to the required limit.
→ sys.maxsize() fetches the largest value a variable of data type Py_ssize_t can store.
Resources:
This is all about the sys module in python.
I think this is easy to know the concept in my blog.:)
Check and change the Python recursion limit (e.g. sys.setrecursionlimit)
Money and Business
In Python, there is an upper limit to the number of recursions (the maximum number of recursions). To execute a recursive function with a large number of calls, it is necessary to change the limit. Use the functions in the sys module of the standard library.
The number of recursions is also limited by the stack size. In some environments, the resource module of the standard library can be used to change the maximum stack size (it worked on Ubuntu, but not on Windows or mac).
The following information is provided here.
- Get the upper limit of the current number of recursions: sys.getrecursionlimit()
- Change the upper limit of the number of recursions: sys.setrecursionlimit()
- Change the maximum size of the stack: resource.setrlimit()
The sample code is running on Ubuntu.
Get the current recursion limit: sys.getrecursionlimit()
The current recursion limit can be obtained with sys.getrecursionlimit().
In the example, the maximum number of recursions is 1000, which may vary depending on your environment. Note that the resource we are importing here will be used later, but not on Windows.
As an example, we will use the following simple recursive function. If a positive integer n is specified as an argument, the number of calls will be n times.
An error (RecursionError) will be raised if you try to perform recursion more than the upper limit.
Note that the value obtained by sys.getrecursionlimit() is not strictly the maximum number of recursions, but the maximum stack depth of the Python interpreter, so even if the number of recursions is slightly less than this value, an error (RecursionError) will be raised.
Change recursion limit: sys.setrecursionlimit()
The upper limit of the number of recursions can be changed by sys.setrecursionlimit(). The upper limit is specified as an argument.
Allows deeper recursion to be performed.
If the specified upper limit is too small or too large, an error will occur. This constraint (upper and lower limits of the limit itself) varies depending on the environment.
The maximum value of limit depends on the platform. If you need deep recursion, you can specify a larger value within the range supported by the platform, but be aware that this value will cause a crash if it is too large.
If the new limit is too low at the current recursion depth, a RecursionError exception is raised.
sys.setrecursionlimit() — System-specific parameters and functions — Python 3.10.0 Documentation
The maximum number of recursions is also limited by the stack size, as explained next.
Change the maximum size of the stack: resource.setrlimit()
Even if a large value is set in sys.setrecursionlimit(), it may not be executed if the number of recursions is large. A segmentation fault occurs as follows.
In Python, the resource module in the standard library can be used to change the maximum stack size. However, the resource module is a Unix-specific module and cannot be used on Windows.
With resource.getrlimit(), you can get the limit of the resource specified in the argument as a tuple of (soft limit, hard limit). Here, we specify resource.RLIMIT_STACK as the resource, which represents the maximum size of the call stack of the current process.
In the example, the soft limit is 8388608 (8388608 B = 8192 KB = 8 MB) and the hard limit is -1 (unlimited).
You can change the limit of the resource with resource.setrlimit(). Here, the soft limit is also set to -1 (no limit). You can also use the constant resource.RLIM_INFINIT to represent the unlimited limit.
Deep recursion, which could not be performed due to segmentation fault before the stack size change, can now be performed.
Here, the soft limit is set to -1 (no limit) for a simple experiment, but in reality, it would be safer to limit it to an appropriate value.
In addition, when I tried to set an unlimited soft limit on my mac as well, the following error occurred. ValueError: not allowed to raise maximum limit
Running the script with sudo didn't help. It may be restricted by the system.
A process with the effective UID of a superuser can request any reasonable limit, including no limit.
However, a request that exceeds the limit imposed by the system will still result in a ValueError.
resource.setrlimit() — Resource usage information — Python 3.10.0 Documentation
Windows doesn't have a resource module, and mac couldn't change the maximum stack size due to system limitations. If we can increase the stack size by some means, we should be able to solve the segmentation fault, but we have not been able to confirm this.
How to set the recursion limit in Python
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What is the recursion limit?
Recursion is a process by which a function calls itself, directly or indirectly. Every time a function is invoked, a new frame is added to the stack.
To avoid infinite recursion leading to the overflowing of the stack, every programming language has a recursion limit. This limit varies is programming languages and is platform dependent.
The sys module
The sys module provides access to the system-specific parameters and functions that interact and are maintained by the Python interpreter.
The setrecursionlimit() method
The setrecursionlimit() method of the sys module sets the maximum recursion depth of the Python interpreter.
Note: Depending on the program and platform, we can set a higher recursion limit. However, very high limits can cause the interpreter to crash.
This method raises a RecursionError when the given limit is too low at the current recursion depth.
Get and Increase the Maximum Recursion Depth in Python
This article will introduce methods to get and increase the maximum recursion depth in Python with the getrecursionlimit() and setrecursionlimit() functions.
Use the getrecursionlimit() Function to Get the Maximum Recursion Depth in Python
What is recursion? Recursion is the process of repetition.
In Python, we have some limits for recursive functions. It tells about how many times the function will repeat. We can use getrecursionlimit() function to get the maximum recursion depth. The correct syntax is:
This method accepts no parameters.
The program below shows how we can use this method to get the maximum recursion limit in Python.
Use the setrecursionlimit() Function to Set the Maximum Recursion Depth in Python
If the recursion depth exceeds the default maximum recursion depth in Python, it will throw a RecursionError . Let’s see the below example.
We need to increase the maximum recursion depth to solve the above issue. We use setrecursionlimit() function to set the recursion limit. The correct syntax to use this function is as follows:
This method accepts one parameter only. The detail of its parameter is as follows:
The program below shows how we can use this method to set the recursion limit in Python.