Improve dataset card: document schema, measured stats and limitations

README.md

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+---
+configs:
+- config_name: default
+  data_files:
+  - split: train
+    path: data/train-*
+dataset_info:
+  features:
+  - name: repo_name
+    dtype: string
+  - name: path
+    dtype: string
+  - name: copies
+    dtype: string
+  - name: size
+    dtype: string
+  - name: content
+    dtype: string
+  - name: license
+    dtype: string
+  - name: hash
+    dtype: int64
+  - name: line_mean
+    dtype: float64
+  - name: line_max
+    dtype: int64
+  - name: alpha_frac
+    dtype: float64
+  - name: autogenerated
+    dtype: bool
+  - name: ratio
+    dtype: float64
+  - name: config_test
+    dtype: bool
+  - name: has_no_keywords
+    dtype: bool
+  - name: few_assignments
+    dtype: bool
+  splits:
+  - name: train
+    num_bytes: 432490836
+    num_examples: 45961
+  download_size: 159490243
+  dataset_size: 432490836
+license: other
+language:
+- code
+tags:
+- code
+- python
+- filtered
+size_categories:
+- 10K<n<100K
+---
+
+# code-valid
+
+45,961 Python files that passed a code-quality filtering pass, each kept with its
+source repository, file path, declared licence, and the filter values that were
+computed on it.
+
+## At a glance
+
+| | |
+|---|---|
+| Rows | 45,961 (single `train` split) |
+| File type | Python only — `.py` for **100%** of rows |
+| Columns | 15 (see below) |
+| Parquet on disk | 159.5 MB (432.5 MB uncompressed) |
+| Row groups | 5 |
+
+## Columns
+
+| Column | Type | What it holds |
+|---|---|---|
+| `repo_name` | string | source repository, e.g. `pansapiens/mytardis` |
+| `path` | string | file path in the repository, e.g. `tardis/apps/mx_views/views.py` |
+| `content` | string | the file's full source text (mean 9,272 chars, median 3,937, max 644,045) |
+| `license` | string | SPDX-style licence string of the repository |
+| `size` | string | file size in bytes, as a string (1,024 – 895,755; mean 9,231) |
+| `copies` | string | in how many repositories the same content was found (1 for 44,880 rows, up to 11) |
+| `hash` | int64 | content hash used for the duplicate check |
+| `line_mean` | float64 | mean line length (6.5 – 99.9, mean 33.8) |
+| `line_max` | int64 | longest line |
+| `alpha_frac` | float64 | fraction of alphabetic characters (0.25 – 0.96, mean 0.60) |
+| `ratio` | float64 | filter ratio value (1.50 – 13.56, mean 3.70) |
+| `autogenerated` | bool | `False` in **every** row of this snapshot |
+| `config_test` | bool | `True` in 5,104 rows (11%) |
+| `has_no_keywords` | bool | `True` in 301 rows |
+| `few_assignments` | bool | `False` in **every** row of this snapshot |
+
+## Licence distribution
+
+Counted over all 45,961 rows — 15 distinct values, no nulls:
+
+| Licence | Rows |
+|---|---|
+| `mit` | 14,285 |
+| `apache-2.0` | 8,216 |
+| `gpl-3.0` | 8,188 |
+| `gpl-2.0` | 4,708 |
+| `bsd-3-clause` | 4,650 |
+| `agpl-3.0` | 2,307 |
+| `bsd-2-clause` | 1,224 |
+| `lgpl-3.0` | 806 |
+| `lgpl-2.1` | 580 |
+| `unlicense` | 328 |
+| `mpl-2.0` | 273 |
+| `isc` | 162 |
+| `cc0-1.0` | 135 |
+| `epl-1.0` | 77 |
+| `artistic-2.0` | 22 |
+
+## Usage
+
+```python
+from datasets import load_dataset
+
+ds = load_dataset("razhan/code-valid", split="train")
+row = ds[0]
+print(row["repo_name"], row["path"], row["license"])
+print(row["content"][:300])
+```
+
+If you need only permissively licensed code, filter on `license` in
+`{"mit", "apache-2.0", "bsd-2-clause", "bsd-3-clause", "isc", "unlicense", "cc0-1.0"}`
+— that keeps exactly 29,000 rows. Copyleft licences account for the remaining 16,589.
+
+## Known limitations
+
+- **Licence is per repository, not per file.** Rows inherit the repository's
+  declared licence; verify before redistribution, and note that 16,589 rows carry
+  copyleft licences (`gpl-*`, `agpl-3.0`, `lgpl-*`).
+- Duplicate content is not removed: `copies` > 1 for 1,081 rows, and those rows
+  appear once per repository.
+- The flag columns record a single filtering pass from 2022; `autogenerated` and
+  `few_assignments` are constant `False` here, so they carry no signal in this
+  snapshot.
+- No language/version metadata beyond "it parses as Python", and no repository
+  snapshot date — code drift between the crawl and today is not tracked.
+- Some files are minified, generated, or vendor dumps that survived the filters
+  applied at the time.