Add error message on invalid column

Add an error message that is printed when the user supplies an invalid
column to prevent unwanted calculations and user-visible exceptions.

Also add tests to ensure that the error message is printed to stderr.

Closes #1

blendplot/__main__.py

@@ -2,6 +2,7 @@
 A cli application for plotting 3D data in obj format for use in Blender.
 """
 import cli.app
+import sys
 import time
 
 from . import obj_graph
@@ -70,8 +71,11 @@ def main(input_filename, output_filename, num_rows, columns, spacing, point_size
     end = time.time()
     output_file.close()
 
-    print("Wrote plot file to %s" % output_filename)
-    print("Plotted %s points in %f seconds" % (points, end - start))
+    if points is None:
+        sys.exit(1)
+    else:
+        print("Wrote plot file to %s" % output_filename)
+        print("Plotted %s points in %f seconds" % (points, end - start))
 
 def run():
     blendplot.run()

blendplot/obj_graph.py

@@ -3,6 +3,7 @@
 """
 from sklearn import preprocessing
 import pandas as pd
+import sys
 
 def add_cube_verticies(cube_str, x, y, z, point_size):
     """
@@ -170,9 +171,20 @@ def plot_file(input_filename, output_file, num_rows, columns, spacing, point_siz
     Returns
     -------
     points : int
-        the number of points that were plotted
+        the number of points that were plotted, or None if the plot is unable
+        to be made
     """
     original_data = pd.read_csv(input_filename, nrows = num_rows)
+
+    missing = get_missing_columns(original_data, columns, category_column)
+    if len(missing) > 0:
+        missing_columns = ", ".join(missing)
+        valid_columns = ", ".join(list(original_data.columns))
+        error_msg = "Invalid column(s): %s\n" % missing_columns
+        error_msg += "Valid columns are: %s" % valid_columns
+        print(error_msg, file=sys.stderr)
+        return None
+
     data = pd.DataFrame(original_data, columns = columns).dropna()
     data = pd.DataFrame(preprocessing.scale(data), columns = data.columns)
 
@@ -196,3 +208,32 @@ def plot_file(input_filename, output_file, num_rows, columns, spacing, point_siz
 
     points = num_rows if num_rows is not None else len(data.index)
     return points
+
+def get_missing_columns(data, columns, category_column):
+    """
+    Returns all of the given columns that are not in the given dataframe.
+
+    Parameters
+    ----------
+    columns : List[str]
+        the columns to look for
+    category_column : str
+        the category column to look for, or None if there is no category column
+        being used
+
+    Returns
+    -------
+    missing : List[str]
+        a list of the missing columns
+    """
+    data_columns = set(data.columns)
+
+    if not category_column is None:
+        columns = columns + [category_column]
+
+    missing = []
+    for col in columns:
+        if not col in data_columns:
+            missing.append(col)
+
+    return missing

test/test_obj_graph.py

@@ -5,6 +5,8 @@
 
 from blendplot.obj_graph import *
 
+import utilities
+
 class TestObjGraph(unittest.TestCase):
     def test_add_cube_verticies(self):
         cube_str = ""
@@ -120,6 +122,52 @@ def test_plot_file(self):
 
             self.assertEquals(actual_output, expected_output)
 
+    def test_plot_file_invalid_column(self):
+        input_filename = "test/resources/data_01.csv"
+        output_file = io.StringIO()
+        num_rows = None
+        invalid_column = "u"
+        columns = [invalid_column, "b", "c"]
+        spacing = 0.5
+        point_size = 0.1
+        category_column = None
+
+        func = lambda x: plot_file(input_filename, output_file, num_rows, columns, spacing, point_size, category_column)
+
+        (actual_return, actual_error) = utilities.capture_stderr(func)
+        expected_error = "Invalid column(s): %s\nValid columns are: a, b, c, d, category\n" % invalid_column
+
+        self.assertEquals(actual_error, expected_error)
+        self.assertEquals(actual_return, None)
+
+        actual_output = output_file.getvalue()
+        expected_output = ""
+
+        self.assertEquals(actual_output, expected_output)
+
+    def test_plot_file_invalid_column_multiple(self):
+        input_filename = "test/resources/data_01.csv"
+        output_file = io.StringIO()
+        num_rows = None
+        invalid_columns = ["u", "A"]
+        columns = ["c"] + invalid_columns
+        spacing = 0.5
+        point_size = 0.1
+        category_column = None
+
+        func = lambda x: plot_file(input_filename, output_file, num_rows, columns, spacing, point_size, category_column)
+
+        (actual_return, actual_error) = utilities.capture_stderr(func)
+        expected_error = "Invalid column(s): %s, %s\nValid columns are: a, b, c, d, category\n" % (invalid_columns[0], invalid_columns[1])
+
+        self.assertEquals(actual_error, expected_error)
+        self.assertEquals(actual_return, None)
+
+        actual_output = output_file.getvalue()
+        expected_output = ""
+
+        self.assertEquals(actual_output, expected_output)
+
     def test_plot_file_category(self):
         input_filename = "test/resources/data_01.csv"
         output_file = io.StringIO()
@@ -142,6 +190,28 @@ def test_plot_file_category(self):
 
             self.assertEquals(actual_output, expected_output)
 
+    def test_plot_file_category_invalid(self):
+        input_filename = "test/resources/data_01.csv"
+        output_file = io.StringIO()
+        num_rows = 4
+        columns = ["a", "b", "c"]
+        spacing = 0.5
+        point_size = 0.1
+        invalid_category_column = "cats"
+
+        func = lambda x: plot_file(input_filename, output_file, num_rows, columns, spacing, point_size, invalid_category_column)
+
+        (actual_return, actual_error) = utilities.capture_stderr(func)
+        expected_error = "Invalid column(s): %s\nValid columns are: a, b, c, d, category\n" % invalid_category_column
+
+        self.assertEquals(actual_error, expected_error)
+        self.assertEquals(actual_return, None)
+
+        actual_output = output_file.getvalue()
+        expected_output = ""
+
+        self.assertEquals(actual_output, expected_output)
+
 @given(
   st.text(),
   st.floats(allow_nan=False, allow_infinity=False),

test/utilities.py

@@ -0,0 +1,14 @@
+import io
+import sys
+
+def capture_stderr(func):
+    err, sys.stderr = sys.stderr, io.StringIO()
+    value = None
+    try:
+        ret = func(None)
+        sys.stderr.seek(0)
+        value = (ret, sys.stderr.read())
+    finally:
+        sys.stderr = err
+
+    return value