#62: Fix CSV loader not lazy

pystreamapi/loaders/__csv_loader.py

@@ -3,8 +3,10 @@
 from collections import namedtuple
 from csv import reader
 
+from pystreamapi.loaders.__lazy_file_iterable import LazyFileIterable
 
-def csv(file_path: str, delimiter=',', encoding="utf-8") -> list:
+
+def csv(file_path: str, delimiter=',', encoding="utf-8") -> LazyFileIterable:
     """
     Loads a CSV file and converts it into a list of namedtuples.
 
@@ -15,27 +17,29 @@ def csv(file_path: str, delimiter=',', encoding="utf-8") -> list:
         :param delimiter: The delimiter used in the CSV file.
     """
     file_path = __validate_path(file_path)
+    return LazyFileIterable(lambda: __load_csv(file_path, delimiter, encoding))
+
+
+def __load_csv(file_path, delimiter, encoding):
+    """Load a CSV file and convert it into a list of namedtuples"""
     # skipcq: PTC-W6004
-    with open(file_path, 'r', newline='', encoding=encoding) as csvfile:
+    with open(file_path, mode='r', newline='', encoding=encoding) as csvfile:
         csvreader = reader(csvfile, delimiter=delimiter)
 
         # Create a namedtuple type, casting the header values to int or float if possible
         Row = namedtuple('Row', list(next(csvreader, [])))
 
         # Process the data, casting values to int or float if possible
         data = [Row(*[__try_cast(value) for value in row]) for row in csvreader]
-
     return data
 
 
 def __validate_path(file_path: str):
-    """Validate a path string to prevent path traversal attacks"""
-    if not os.path.isabs(file_path):
-        raise ValueError("The file_path must be an absolute path.")
-
+    """Validate the path to the CSV file"""
     if not os.path.exists(file_path):
         raise FileNotFoundError("The specified file does not exist.")
-
+    if not os.path.isfile(file_path):
+        raise ValueError("The specified path is not a file.")
     return file_path
 
 

pystreamapi/loaders/__lazy_file_iterable.py

@@ -0,0 +1,23 @@
+class LazyFileIterable:
+    """LazyFileIterable is an iterable that loads data from a data source lazily."""
+
+    def __init__(self, loader):
+        self.__loader = loader
+        self.__data = None
+
+    def __iter__(self):
+        self.__load_data()
+        return iter(self.__data)
+
+    def __getitem__(self, index):
+        self.__load_data()
+        return self.__data[index]
+
+    def __len__(self):
+        self.__load_data()
+        return len(self.__data)
+
+    def __load_data(self):
+        """Loads the data from the data source if it has not been loaded yet."""
+        if self.__data is None:
+            self.__data = self.__loader()

tests/test_loaders.py

@@ -1,7 +1,9 @@
 import os
 from unittest import TestCase
+
 from pystreamapi.loaders import csv
 
+
 class TestLoaders(TestCase):
 
     def setUp(self) -> None:
@@ -18,6 +20,10 @@ def test_csv_loader(self):
         self.assertEqual(data[1].attr1, 'a')
         self.assertIsInstance(data[1].attr1, str)
 
+    def test_csv_loader_is_iterable(self):
+        data = csv(f'{self.path}/data.csv')
+        self.assertEqual(len(list(iter(data))), 2)
+
     def test_csv_loader_with_custom_delimiter(self):
         data = csv(f'{self.path}/data2.csv', delimiter=';')
         self.assertEqual(len(data), 1)
@@ -32,6 +38,6 @@ def test_csv_loader_with_invalid_path(self):
         with self.assertRaises(FileNotFoundError):
             csv(f'{self.path}/invalid.csv')
 
-    def test_csv_loader_with_non_absolute_path(self):
+    def test_csv_loader_with_non_file(self):
         with self.assertRaises(ValueError):
-            csv('invalid.csv')
+            csv(f'{self.path}/')