Add data export to various formats (#151)

* add export function

* include more formats

* add docs

docs/source/data_access.rst

@@ -65,4 +65,26 @@ for getting the session or the engine:
 
 .. autofunction:: mendeleev.db.get_session
 
-.. autofunction:: mendeleev.db.get_engine
+.. autofunction:: mendeleev.db.get_engine
+
+
+Export data
+-----------
+
+The data can be exported to a number of formats using the CLI by invoking `inv export` command. The following formats are supported:
+
+- csv
+- json
+- html
+- markdown
+
+The command will export all the tables from the database to a set of files in the specified format.
+
+In order to use this functionality you'll need to clone the mendeleev repository and install the package in the development mode. Here's how you can do it:
+
+```bash
+gh clone lmmentel/mendeleev
+cd mendeleev
+poetry install
+poetry run inv export
+```

pyproject.toml

@@ -58,6 +58,7 @@ sphinx-copybutton = "^0.3.1"
 sphinx-material = "^0.0.32"
 sphinxcontrib-bibtex = "^2.1.4"
 pre-commit = "==3.5.0"
+invoke = "^2.2.0"
 
 [tool.poetry.group.vis]
 optional = true

tasks.py

@@ -0,0 +1,45 @@
+from pathlib import Path
+from invoke import task
+
+
+@task
+def export(c):
+    """Export data to a few formats files."""
+    tables = [
+        "elements",
+        "groups",
+        "ionicradii",
+        "ionizationenergies",
+        "isotopedecaymodes",
+        "isotopes",
+        "oxidationstates",
+        "phasetransitions",
+        "screeningconstants",
+        "series",
+    ]
+
+    formats = [
+        "csv",
+        "html",
+        "json",
+        "markdown",
+    ]
+
+    for fmt in formats:
+        Path(f"data/{fmt}").mkdir(exist_ok=True)
+        for table in tables:
+            print(f"Exporting {table} to {fmt} ... ", end="")
+            c.run(
+                f"sqlite3 -{fmt} mendeleev/elements.db 'SELECT * FROM {table};' > data/{fmt}/{table}.{fmt}",
+                echo=True,
+            )
+            print("done")
+
+    # SQL dump
+    print("Creating SQL files with the data ... ", end="")
+    c.run(
+        "sqlite3 mendeleev/elements.db .dump > data/sql/elements.sql",
+        echo=True,
+        pty=True,
+    )
+    print("done")