diff --git a/app/constants.py b/app/constants.py
index dfdda1f..ae6a9bb 100644
--- a/app/constants.py
+++ b/app/constants.py
@@ -1,20 +1,20 @@
-datasets = [
+DATASETS = [
     "coronavirus-commercants-parisiens-livraison-a-domicile",
     "deconfinement-pistes-cyclables-temporaires",
     "deconfinement-parking-relais-doublement-des-places",
 ]
-url = "https://opendata.paris.fr/api/records/1.0/search/?dataset={}&q=&rows=-1"
-filenames = {
+URL = "https://opendata.paris.fr/api/records/1.0/search/?dataset={}&q=&rows=-1"
+FILENAMES = {
     "coronavirus-commercants-parisiens-livraison-a-domicile": "home-delivery",
     "deconfinement-pistes-cyclables-temporaires": "cycling-paths",
     "deconfinement-parking-relais-doublement-des-places": "relay-parking",
 }
-files = {
+FILES = {
     "cycling-paths": "data/cycling-paths.json",
     "relay-parking": "data/relay-parking.json",
     "home-delivery": "data/home-delivery.json",
 }
-columns = {
+COLUMNS = {
     "cycling-paths": ["geo_shape", "statut", "record_timestamp", "complement"],
     "relay-parking": [
         "societe",
diff --git a/app/preprocessing.py b/app/preprocessing.py
index 34169b7..bd451dc 100644
--- a/app/preprocessing.py
+++ b/app/preprocessing.py
@@ -1,20 +1,27 @@
 from json import load
 from pandas import json_normalize, DataFrame
-from constants import files, columns
+from constants import FILES, COLUMNS
 
 
-def open_json(dataset):
-    with open(files[dataset]) as f:
+def open_json(dataset) -> dict:
+    """
+    Loads a dictionary with data from a JSON file
+    """
+    with open(FILES[dataset]) as f:
         json = load(f)
     return json
 
 
-def create_dataframe(dataset):
+def create_dataframe(dataset) -> DataFrame:
+    """
+    Creates a DataFrame from a JSON file
+    """
     json = open_json(dataset)
     df = json_normalize(
-        data=json["records"],
-        record_path=["fields"],
-        meta=columns[dataset],
-        errors="ignore",
+        data=json, record_path=["records"], meta=COLUMNS[dataset], errors="ignore",
     )
+    print(df)
     return df
+
+
+create_dataframe("cycling-paths")
diff --git a/app/request_datasets.py b/app/request_datasets.py
index 0445acc..8b35600 100644
--- a/app/request_datasets.py
+++ b/app/request_datasets.py
@@ -1,28 +1,34 @@
-from constants import datasets, url
+from json import dump
 from requests import get
-from constants import datasets, url, filenames
-from requests import get, codes
-from json import dump, dumps
+from constants import FILENAMES, URL
 
 
-def save_json(data, filename):
+def format_url(dataset) -> str:
+    """
+    Constructs the API's URL for the requested dataset
+    """
+    link = URL.format(dataset)
+    return link
+
+
+def save_json(data, dataset):
+    """
+    Dumps the data into a JSON file
+    """
     data_dir = "data/"
-    with open(data_dir + filename + ".json", "w") as f:
+    with open(data_dir + FILENAMES[dataset] + ".json", "w") as f:
         dump(data, f, ensure_ascii=False)
 
 
-def request_dataset(url, filename):
+def request_dataset(dataset):
+    """
+    Fetches the requested dataset from opendata's API
+    """
+    url = format_url(dataset)
     response = get(url)
     response.raise_for_status()
     data = response.json()
-    save_json(data, filename)
+    save_json(data=data, dataset=dataset)
 
 
-def format_url():
-    for set in datasets:
-        link = url.format(set)
-        request_dataset(link, filenames[set])
-
-
-if __name__ == "__main__":
-    format_url()
+request_dataset("deconfinement-pistes-cyclables-temporaires")
diff --git a/shell.nix b/shell.nix
index c32bc53..589b92a 100644
--- a/shell.nix
+++ b/shell.nix
@@ -17,5 +17,6 @@ pkgs.mkShell {
     python-language-server
     pyls-black
     pyls-isort
+    pyls-mypy
   ];
 }