Reading Python File-Like Objects from C | Python Last Updated : 07 Jun, 2019 Summarize Comments Improve Suggest changes Share Like Article Like Report Writing C extension code that consumes data from any Python file-like object (e.g., normal files, StringIO objects, etc.). read() method has to be repeatedly invoke to consume data on a file-like object and take steps to properly decode the resulting data. Given below is a C extension function that merely consumes all of the data on a file-like object and dumps it to standard output. Code #1 : CPP #define CHUNK_SIZE 8192 /* Consume a "file-like" object and write bytes to stdout */ static PyObject* py_consume_file(PyObject* self, PyObject* args) { PyObject* obj; PyObject* read_meth; PyObject* result = NULL; PyObject* read_args; if (!PyArg_ParseTuple(args, "O", &obj)) { return NULL; } /* Get the read method of the passed object */ if ((read_meth = PyObject_GetAttrString(obj, "read")) == NULL) { return NULL; } /* Build the argument list to read() */ read_args = Py_BuildValue("(i)", CHUNK_SIZE); while (1) { PyObject* data; PyObject* enc_data; char* buf; Py_ssize_t len; /* Call read() */ if ((data = PyObject_Call(read_meth, read_args, NULL)) == NULL) { goto final; } /* Check for EOF */ if (PySequence_Length(data) == 0) { Py_DECREF(data); break; } /* Encode Unicode as Bytes for C */ if ((enc_data = PyUnicode_AsEncodedString(data, "utf-8", "strict")) == NULL) { Py_DECREF(data); goto final; } /* Extract underlying buffer data */ PyBytes_AsStringAndSize(enc_data, &buf, &len); /* Write to stdout (replace with something more useful) */ write(1, buf, len); /* Cleanup */ Py_DECREF(enc_data); Py_DECREF(data); } result = Py_BuildValue(""); final: /* Cleanup */ Py_DECREF(read_meth); Py_DECREF(read_args); return result; } A file-like object such as a StringIO instance is prepared to test the code and then it is passed in: Code #2 : Python3 1== import io f = io.StringIO('Hello\nWorld\n') import sample sample.consume_file(f) Output : Hello World Unlike a normal system file, a file-like object is not necessarily built around a low-level file descriptor. Thus, a normal C library functions can't be used to access it. Instead, a Python’s C API is used to manipulate the file-like object much like you would in Python. So, the read() method is extracted from the passed object. An argument list is built and then repeatedly passed to PyObject_Call() to invoke the method. To detect end-of-file (EOF), PySequence_Length() is used to see if the returned result has zero length. For all I/O operations, the concern is underlying encoding and distinction between bytes and Unicode. This recipe shows how to read a file in text mode and decode the resulting text into a bytes encoding that can be used by C. If the file is read in binary mode, only minor changes will be made as shown in the code below. Code #3 : CPP /* Call read() */ if ((data = PyObject_Call(read_meth, read_args, NULL)) == NULL) { goto final; } /* Check for EOF */ if (PySequence_Length(data) == 0) { Py_DECREF(data); break; } if (!PyBytes_Check(data)) { Py_DECREF(data); PyErr_SetString(PyExc_IOError, "File must be in binary mode"); goto final; } /* Extract underlying buffer data */ PyBytes_AsStringAndSize(data, &buf, &len); Comment More infoAdvertise with us Next Article Reading Python File-Like Objects from C | Python M manikachandna97 Follow Improve Article Tags : Python Python-ctype Practice Tags : python Similar Reads Python Tutorial - Learn Python Programming Language Python is one of the most popular programming languages. Itâs simple to use, packed with features and supported by a wide range of libraries and frameworks. Its clean syntax makes it beginner-friendly. It'sA high-level language, used in web development, data science, automation, AI and more.Known fo 10 min read Python Interview Questions and Answers Python is the most used language in top companies such as Intel, IBM, NASA, Pixar, Netflix, Facebook, JP Morgan Chase, Spotify and many more because of its simplicity and powerful libraries. To crack their Online Assessment and Interview Rounds as a Python developer, we need to master important Pyth 15+ min read Python OOPs Concepts Object Oriented Programming is a fundamental concept in Python, empowering developers to build modular, maintainable, and scalable applications. By understanding the core OOP principles (classes, objects, inheritance, encapsulation, polymorphism, and abstraction), programmers can leverage the full p 11 min read Python Projects - Beginner to Advanced Python is one of the most popular programming languages due to its simplicity, versatility, and supportive community. Whether youâre a beginner eager to learn the basics or an experienced programmer looking to challenge your skills, there are countless Python projects to help you grow.Hereâs a list 10 min read Python Exercise with Practice Questions and Solutions Python Exercise for Beginner: Practice makes perfect in everything, and this is especially true when learning Python. If you're a beginner, regularly practicing Python exercises will build your confidence and sharpen your skills. To help you improve, try these Python exercises with solutions to test 9 min read Python Programs Practice with Python program examples is always a good choice to scale up your logical understanding and programming skills and this article will provide you with the best sets of Python code examples.The below Python section contains a wide collection of Python programming examples. These Python co 11 min read Python Introduction Python was created by Guido van Rossum in 1991 and further developed by the Python Software Foundation. It was designed with focus on code readability and its syntax allows us to express concepts in fewer lines of code.Key Features of PythonPythonâs simple and readable syntax makes it beginner-frien 3 min read Python Data Types Python Data types are the classification or categorization of data items. It represents the kind of value that tells what operations can be performed on a particular data. Since everything is an object in Python programming, Python data types are classes and variables are instances (objects) of thes 9 min read Input and Output in Python Understanding input and output operations is fundamental to Python programming. With the print() function, we can display output in various formats, while the input() function enables interaction with users by gathering input during program execution. Taking input in PythonPython input() function is 8 min read Enumerate() in Python enumerate() function adds a counter to each item in a list or other iterable. It turns the iterable into something we can loop through, where each item comes with its number (starting from 0 by default). We can also turn it into a list of (number, item) pairs using list().Let's look at a simple exam 3 min read Like