Quark's Outlines: Python Files

Quark's Outlines: Python Files ## An Overview of Python Files ## What is a Python file? ## Problem: open and close Python files ## What can you do with a Python file? ## How are file objects connected to system files? ## A Historical Timeline of Python Files ## People connected programs to files. ## People added file objects to Python. ## People made file access safer. ## Problems & Solutions with Python Files ## Problem: How do you read a saved file in Python? ## Problem: How do you write a log to disk in Python? ## Problem: How do you write multiple lines at once in Python? ## Problem: How do you read one line at a time in Python? ## Problem: How do you write and read binary data in Python? ## Like, Comment, Share, and Subscribe Overview, Historical Timeline, Problems & Solutions You use Python files to read, write, or process data stored on disk. A Python file object connects your code to an open file. This object wraps a system file handle and gives you a way to work with text or binary data. When you open a file, Python gives you a file object. You can use that object to read contents, write new data, or move through the file. When you finish, you must close the file to free system resources. Python lets you open a file and read its contents. If the file hello.txt contains Hello, world!, this prints: Hello, world! To open a file, call the built-in open() function. You pass the filename and a mode like "r" (read), "w" (write), or "a" (append). The open() call gives you a file object. To close a file, use the close() method. This releases the file handle. A better way is to use the with statement. This keeps the file open only inside a block and closes it when done. Python helps you manage files using the with statement. This prints the file content and closes it when done. Once you open a file, you can use methods like read(), readline(), and readlines() to get content. You can also use write() or writelines() to store new data. These methods depend on the mode you choose when opening the file. Python gives you read and write methods for files. This writes two lines to the file data.txt. A Python file is a high-level object. Under the surface, it wraps a C-level file pointer. The sys.stdin, sys.stdout, and sys.stderr objects are file objects linked to standard input, output, and error streams. Python wraps system streams using file objects. This writes: Output to screen Where do Python's file objects come from? Python file objects follow the structure of system-level file handles in C. Over time, the Python language added safer ways to open and close files using the with block. This timeline shows how people built the Python file system one step at a time. 1970 — File pointers in C The stdio library introduced file objects using FILE * handles in C. These became the model for later high-level file access. 1985 — File-like objects in ABC The ABC language, a source of Python ideas, used file-like objects to simplify I/O for beginners. 1991 — Built-in file support Python 0.9.0 added the open() function to create file objects and methods like read() and write(). 1997 — sys.stdin, stdout, stderr Python exposed standard I/O as file objects to match system streams. 2005 — Context managers and with Python 2.5 added with open(...) to ensure files are closed correctly. This reduced bugs caused by missing close() calls. 2010 — Unicode file support Python 3.x made file I/O work smoothly with text encodings like UTF-8. How do you use Python file objects the right way? Python file objects help you load and store information in programs. These examples show how files solve real needs by giving you a clean way to access data stored on disk. You have saved a short message in a file called hello.txt. Now you want your Python code to read that message and display it. You try to open the file and print its content, but you forget to close it or get an error if the file is missing. Problem: You want to read a file and show its contents safely. Solution: Use with open(...) as to read and close the file automatically. Python lets you read file contents safely using with. If hello.txt contains Welcome!, this prints: Welcome! You are building a Python script that records when a task runs. You want to write each run to a file. If the file already exists, you want to add new lines at the end without deleting the old ones. Problem: You want to add lines to an existing file. Solution: Use the "a" mode with open() to append data. Python lets you append text to a file using open in append mode. This adds Task completed to the file without deleting earlier content. You want to store a short list of tasks in a file. Each task should be on a separate line. Writing them one by one is slow and can be messy. Problem: You want to write many lines to a file in one step. Solution: Use the writelines() method to store a list of strings. Python lets you write many lines at once using writelines. This writes all tasks into tasks.txt, each on its own line. You have a large file and want to process each line without loading the whole file into memory. You also want to stop after reading the first few lines. Problem: You want to read a file line by line. Solution: Use a for loop to read the file one line at a time. Python lets you read lines one by one using a for loop. This prints the first three lines of data.txt, without loading the full file. You want to save a picture or other binary file. You know that text mode will not work because the file may contain characters that do not map to readable text. Problem: You need to write binary content to a file. Solution: Use binary mode "wb" or "rb" for writing or reading. Python lets you write binary data using open in binary mode. This writes the start of a PNG file to disk as binary. Did you find this helpful? Let me know by clicking the like button below. I'd love to hear your thoughts in the comments, too! If you want to see more content like this, don't forget to subscribe. Thanks for reading! Mike Vincent is an American software engineer and app developer from Los Angeles, California. More about Mike Vincent Templates let you quickly answer FAQs or store snippets for re-use. Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink. Hide child comments as well For further actions, you may consider blocking this person and/or reporting abuse CODE_BLOCK: f = open("hello.txt", "r") text = f.read() f.close() print(text) Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: f = open("hello.txt", "r") text = f.read() f.close() print(text) CODE_BLOCK: f = open("hello.txt", "r") text = f.read() f.close() print(text) CODE_BLOCK: with open("hello.txt", "r") as f: print(f.read()) Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: with open("hello.txt", "r") as f: print(f.read()) CODE_BLOCK: with open("hello.txt", "r") as f: print(f.read()) CODE_BLOCK: with open("data.txt", "w") as f: f.write("Hello\n") f.write("World\n") Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: with open("data.txt", "w") as f: f.write("Hello\n") f.write("World\n") CODE_BLOCK: with open("data.txt", "w") as f: f.write("Hello\n") f.write("World\n") CODE_BLOCK: import sys sys.stdout.write("Output to screen\n") Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: import sys sys.stdout.write("Output to screen\n") CODE_BLOCK: import sys sys.stdout.write("Output to screen\n") CODE_BLOCK: with open("hello.txt", "r") as f: print(f.read()) Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: with open("hello.txt", "r") as f: print(f.read()) CODE_BLOCK: with open("hello.txt", "r") as f: print(f.read()) CODE_BLOCK: with open("log.txt", "a") as f: f.write("Task completed\n") Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: with open("log.txt", "a") as f: f.write("Task completed\n") CODE_BLOCK: with open("log.txt", "a") as f: f.write("Task completed\n") CODE_BLOCK: lines = ["Buy milk\n", "Call mom\n", "Walk dog\n"] with open("tasks.txt", "w") as f: f.writelines(lines) Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: lines = ["Buy milk\n", "Call mom\n", "Walk dog\n"] with open("tasks.txt", "w") as f: f.writelines(lines) CODE_BLOCK: lines = ["Buy milk\n", "Call mom\n", "Walk dog\n"] with open("tasks.txt", "w") as f: f.writelines(lines) CODE_BLOCK: with open("data.txt", "r") as f: for i, line in enumerate(f): print(line.strip()) if i == 2: break Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: with open("data.txt", "r") as f: for i, line in enumerate(f): print(line.strip()) if i == 2: break CODE_BLOCK: with open("data.txt", "r") as f: for i, line in enumerate(f): print(line.strip()) if i == 2: break CODE_BLOCK: data = b"\x89PNG\r\n\x1a\n" with open("image.png", "wb") as f: f.write(data) Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: data = b"\x89PNG\r\n\x1a\n" with open("image.png", "wb") as f: f.write(data) CODE_BLOCK: data = b"\x89PNG\r\n\x1a\n" with open("image.png", "wb") as f: f.write(data)