replace with double quotes

tests/examples_arguments_syntax/arrow_vector.py

@@ -12,21 +12,21 @@
 vector1 = [0, 0, 3, -1]
 vector2 = [0, 0, 2, 3]
 
-v = pd.DataFrame([vector1, vector2], columns=['x1','y1','x2','y2'])
+v = pd.DataFrame([vector1, vector2], columns=["x1","y1","x2","y2"])
 
 # calculate the vector
-v['x_'] = v['x2'] - v["x1"]
-v['y_'] = v['y2'] - v["y1"]
+v["x_"] = v["x2"] - v["x1"]
+v["y_"] = v["y2"] - v["y1"]
 
 # calculate the angle between current vector and the default point mark direction (0,1)
 # dot product = (x_,y_) dot (0,1) = y_
-v["norm"] = np.sqrt(v['x_']**2 + v['y_']**2)
-v["theta"] = np.degrees(np.arccos(v['y_']/v["norm"] ))
+v["norm"] = np.sqrt(v["x_"]**2 + v["y_"]**2)
+v["theta"] = np.degrees(np.arccos(v["y_"]/v["norm"] ))
 
 
 lines = alt.Chart(v).mark_line().encode(
-    x=alt.X("x1", scale=alt.Scale(domain=(-4, 4)), title='x'),
-    y=alt.Y("y1", scale=alt.Scale(domain=(-4, 4)), title='y'),
+    x=alt.X("x1", scale=alt.Scale(domain=(-4, 4)), title="x"),
+    y=alt.Y("y1", scale=alt.Scale(domain=(-4, 4)), title="y"),
     x2="x2",
     y2="y2"
 )
@@ -36,7 +36,7 @@
     y="y2",
     angle=alt.Angle("theta", scale=alt.Scale(domain=[0, 360])),
     size=alt.value(300),
-    color=alt.value('#000000')
+    color=alt.value("#000000")
 )
 
-lines + wedge
+lines + wedge