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|  | 1 | +--- | 
|  | 2 | +Title: 'with' | 
|  | 3 | +Description: 'Simplifies resource management by automatically handling setup and teardown actions using context managers.' | 
|  | 4 | +Subjects: | 
|  | 5 | +  - 'Computer Science' | 
|  | 6 | +  - 'Data Science' | 
|  | 7 | +Tags: | 
|  | 8 | +  - 'Files' | 
|  | 9 | +  - 'Python' | 
|  | 10 | +CatalogContent: | 
|  | 11 | +  - 'learn-python-3' | 
|  | 12 | +  - 'paths/computer-science' | 
|  | 13 | +--- | 
|  | 14 | + | 
|  | 15 | +The **`with`** keyword in Python is used to wrap the execution of a block of code within methods defined by a context manager. It simplifies resource management — automatically handling setup and teardown operations like opening and closing files, acquiring and releasing locks, or connecting and disconnecting from databases. | 
|  | 16 | + | 
|  | 17 | +When a block under `with` is executed: | 
|  | 18 | + | 
|  | 19 | +1. The context manager’s `__enter__()` method is called. | 
|  | 20 | +2. The block of code inside the `with` statement runs. | 
|  | 21 | +3. The context manager’s `__exit__()` method is automatically called after the block finishes — even if an error occurs. | 
|  | 22 | + | 
|  | 23 | +## Syntax | 
|  | 24 | + | 
|  | 25 | +```pseudo | 
|  | 26 | +with expression [as variable]: | 
|  | 27 | +  # Code block | 
|  | 28 | +``` | 
|  | 29 | + | 
|  | 30 | +**Parameters:** | 
|  | 31 | + | 
|  | 32 | +- `expression`: A context manager that defines `__enter__()` and `__exit__()` methods. | 
|  | 33 | +- `variable` (optional): The object returned by the `__enter__()` method, which can be used inside the code block. | 
|  | 34 | + | 
|  | 35 | +**Return value:** | 
|  | 36 | + | 
|  | 37 | +Returns the object provided by the context manager’s `__enter__()` method, if assigned using `as`. | 
|  | 38 | + | 
|  | 39 | +## Example 1: Managing File Resources | 
|  | 40 | + | 
|  | 41 | +In this example, a file is opened, written to, and automatically closed after the block finishes: | 
|  | 42 | + | 
|  | 43 | +```py | 
|  | 44 | +with open("example.txt", "w") as file: | 
|  | 45 | +  file.write("Hello, World!") | 
|  | 46 | +``` | 
|  | 47 | + | 
|  | 48 | +The output of this code is: | 
|  | 49 | + | 
|  | 50 | +```shell | 
|  | 51 | +# (No visible output) | 
|  | 52 | +# The file 'example.txt' is written and automatically closed. | 
|  | 53 | +``` | 
|  | 54 | + | 
|  | 55 | +Here the file is automatically opened and closed using `with`. Even if an error occurs while writing, `file.close()` is called automatically. | 
|  | 56 | + | 
|  | 57 | +## Example 2: Using Multiple Context Managers | 
|  | 58 | + | 
|  | 59 | +In this example, two files are managed simultaneously, ensuring both are safely opened and closed: | 
|  | 60 | + | 
|  | 61 | +```py | 
|  | 62 | +with open("input.txt", "r") as infile, open("output.txt", "w") as outfile: | 
|  | 63 | +  data = infile.read() | 
|  | 64 | +  outfile.write(data) | 
|  | 65 | +``` | 
|  | 66 | + | 
|  | 67 | +In this example, both files are safely managed, opened at the start, and closed automatically when the block ends. | 
|  | 68 | + | 
|  | 69 | +## Example 3: File Handling with `with` | 
|  | 70 | + | 
|  | 71 | +In this example, data is written to a file and then read back using separate `with` blocks for writing and reading: | 
|  | 72 | + | 
|  | 73 | +```py | 
|  | 74 | +# Writing to a file using 'with' | 
|  | 75 | +with open("demo.txt", "w") as file: | 
|  | 76 | +  file.write("Learning Python 'with' keyword!") | 
|  | 77 | + | 
|  | 78 | +# Reading the same file | 
|  | 79 | +with open("demo.txt", "r") as file: | 
|  | 80 | +  content = file.read() | 
|  | 81 | +print(content) | 
|  | 82 | +``` | 
|  | 83 | + | 
|  | 84 | +The expected output is: | 
|  | 85 | + | 
|  | 86 | +```shell | 
|  | 87 | +Learning Python 'with' keyword! | 
|  | 88 | +``` | 
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