A context manager is a general Python mechanism for controlling what happens around a block of code. Although commonly used with files, it is not specific to file handling. The with statement asks an object to establish its context when the block begins and handles managed cleanup when the block ends. section 5.10 section 5.2
A with statement connects an object to a block in a predictable sequence:
- Write with, an object, and an as variable: with object as value:. section 5.10
- At block entry, Python calls the object's __enter__ method when it is defined. section 5.10
- Assign the value returned by __enter__ to the variable after as; files return the file object itself. section 5.10
- Use the object inside the indented block, then let the context-management behavior finish when the block ends. section 5.10
Writing a file safely
The explicit approach opens a file and requires a separate close call. The idiomatic approach keeps the file inside a with block:\n\nwith open('myfile.txt', 'w') as f:\n f.write('abc\\n')\n f.write('def\\n')\n\nHere, f is the value returned by the file object's context setup. When the block ends, the file is flushed and closed without an explicit f.close(). This matters especially when writing files or opening many files, because it conserves resources and ensures closure. section 5.10 section 5.2
with open('myfile.txt', 'w') as f:
f.write('abc\n')
f.write('def\n')
Run the compact file-writing example and inspect the block controlled by with. section 5.10
