WEBVTT 00:00:00.700 --> 00:00:08.083 In this lesson, we will turn a folder of text files into a small inventory, then save an uppercase copy 00:00:08.083 --> 00:00:09.191 of one file. 00:00:09.341 --> 00:00:11.666 The original files stay unchanged. 00:00:11.816 --> 00:00:16.125 Open the downloaded examples folder before running the command. 00:00:16.275 --> 00:00:21.779 All reads use the fixtures directory, and all generated files go into out. 00:00:21.929 --> 00:00:28.946 This separation makes it easy to inspect the result and repeat the demonstration without touching your 00:00:28.946 --> 00:00:29.823 own documents. 00:00:31.970 --> 00:00:34.957 A Path represents a filesystem location. 00:00:35.107 --> 00:00:41.400 A String represents text, so wrap a filename in path when calling these file APIs. 00:00:41.550 --> 00:00:47.289 The name and extension fields are read only, and the extension includes its leading dot. 00:00:47.439 --> 00:00:51.471 A relative data path starts at your current working directory. 00:00:51.621 --> 00:00:55.717 That is why our run instructions first move into examples. 00:00:55.867 --> 00:00:59.941 Later, module imports will have a different relative path rule. 00:01:02.090 --> 00:01:06.634 The files function produces a lazy stream of filesystem entries. 00:01:06.784 --> 00:01:12.075 Our pattern selects text files, including matches below nested directories. 00:01:12.225 --> 00:01:17.643 We explicitly retain regular files, then project each entry to its name. 00:01:17.793 --> 00:01:24.471 Sorting makes our teaching output deterministic instead of depending on directory traversal order. 00:01:24.621 --> 00:01:27.394 Collect consumes the stream and creates a List. 00:01:27.544 --> 00:01:33.837 Notice that a filesystem entry contains metadata; it is not simply a filename string. 00:01:35.990 --> 00:01:39.702 Use read_text when you need one complete text value. 00:01:39.852 --> 00:01:44.183 Use read_lines when your processing works one line at a time. 00:01:44.333 --> 00:01:48.983 Both are text APIs and expect valid UTF eight input. 00:01:49.133 --> 00:01:53.059 Images and archives belong with the byte APIs instead. 00:01:53.209 --> 00:01:58.457 Here, read_lines supplies a stream directly, so we do not add stream after it. 00:01:58.607 --> 00:02:04.751 Each callback returns a transformed line without changing the original file on disk. 00:02:06.900 --> 00:02:09.332 Now add a terminal operation. 00:02:09.482 --> 00:02:14.815 Save_lines consumes the line stream and adds a line ending for each value. 00:02:14.965 --> 00:02:20.043 Create_parents allows the out directory to be created on the first run. 00:02:20.193 --> 00:02:27.297 The documented save operation writes a temporary sibling file and commits the replacement atomically. 00:02:27.447 --> 00:02:30.689 That prevents readers from seeing a half written target. 00:02:30.839 --> 00:02:36.322 It does not mean several different output files become one transaction together. 00:02:38.470 --> 00:02:41.030 Read the saved file back and print it. 00:02:41.180 --> 00:02:46.279 This checks the complete path from discovery and transformation to disk output. 00:02:46.429 --> 00:02:52.061 The uppercase text should contain the same two lines as notes, with their letters changed. 00:02:52.211 --> 00:02:59.379 Trim is only used for clean terminal presentation here; it is not part of the saved transformation. 00:02:59.529 --> 00:03:07.059 Open both files side by side and verify that the input still contains its original lowercase text. 00:03:09.210 --> 00:03:15.866 Write_text replaces the target by default, while append_text adds content to an existing file. 00:03:16.016 --> 00:03:22.693 We intentionally reset our demonstration journal at the start of every run, then append the second line. 00:03:22.843 --> 00:03:25.126 That makes repeated runs predictable. 00:03:25.276 --> 00:03:32.508 Pay attention to the explicit newline characters: a text write receives exactly the text you supply. 00:03:32.658 --> 00:03:39.527 Choose save_lines when your input already consists of separate line values and needs line endings. 00:03:41.680 --> 00:03:48.165 A common mistake is assuming a write will refuse to replace an existing file automatically. 00:03:48.315 --> 00:03:52.198 Set overwrite to false when replacement is not acceptable. 00:03:52.348 --> 00:03:56.636 This deliberate attempt fails because our journal already exists. 00:03:56.786 --> 00:04:02.951 The catch block lets the demonstration continue, and the journal still contains first and second. 00:04:03.101 --> 00:04:05.960 We will study structured errors in lesson nine. 00:04:06.110 --> 00:04:11.379 For now, compare the protected failure with the successful explicit reset above. 00:04:13.530 --> 00:04:18.543 For practice, add a third text file inside fixtures and rerun the script. 00:04:18.693 --> 00:04:24.048 The sorted inventory should grow, while the uppercase copy should still come from notes. 00:04:24.198 --> 00:04:30.342 Then change the selected source to your new fixture and predict its output before running again. 00:04:30.492 --> 00:04:32.241 Keep writes inside out. 00:04:32.391 --> 00:04:40.459 You have now connected Path values, lazy directory traversal, line processing, and controlled saving into 00:04:40.459 --> 00:04:42.610 one useful automation script.