Swap path to bytes

Author: bprobert97

app.py

@@ -61,57 +61,36 @@
 mag_limit = st.sidebar.slider("Magnitude Limit", 1, 8, 5)
 
 # Session state to persist chart path
-if "chart_path" not in st.session_state:
-    st.session_state.chart_path = None
-
-# ───────────────────────────────────────────────
-# Cached plot generator
-# ───────────────────────────────────────────────
-@st.cache_resource(show_spinner=False)
-def generate_plot(plot_type: str, dt: datetime, mag_limit: int) -> str:
-    """Generate and return path to starplot image."""
-    if plot_type == "Horizon":
-        return make_horizon_plot(
-            output_path="images/glasgow_horizon.png",
-            dt=dt,
-            mag_limit=mag_limit,
-            resolution=1600,  # smaller for speed
-        )
-    else:
-        return make_zenith_plot(
-            output_path="images/glasgow_zenith.png",
-            dt=dt,
-            mag_limit=mag_limit,
-            resolution=1600,  # smaller for speed
-        )
+if "chart_bytes" not in st.session_state:
+    st.session_state.chart_bytes = None
 
 # ───────────────────────────────────────────────
 # Generate chart button
 # ───────────────────────────────────────────────
+# Generate chart
 if st.sidebar.button("Generate Chart"):
     tz = ZoneInfo("Europe/London")
     dt = datetime.combine(obs_date, obs_time).replace(tzinfo=tz)
 
     with st.spinner("Generating chart, please wait..."):
-        path = generate_plot(plot_type, dt, mag_limit)
+        if plot_type == "Horizon":
+            img_bytes = make_horizon_plot(dt=dt, mag_limit=mag_limit)
+        else:
+            img_bytes = make_zenith_plot(dt=dt, mag_limit=mag_limit)
 
-    st.session_state.chart_path = path
+    st.session_state.chart_bytes = img_bytes
     st.success("✅ Chart generated!")
 
 # ───────────────────────────────────────────────
 # Display chart + download button
 # ───────────────────────────────────────────────
-if st.session_state.chart_path:
-    st.image(
-        st.session_state.chart_path,
-        caption=f"{plot_type} chart from Glasgow",
-        width="content",
+if st.session_state.chart_bytes:
+    st.image(st.session_state.chart_bytes,
+             caption=f"{plot_type} chart from Glasgow")
+
+    st.download_button(
+        label="⬇️ Download chart",
+        data=st.session_state.chart_bytes,
+        file_name=f"glasgow_{plot_type.lower()}.png",
+        mime="image/png",
     )
-
-    with open(st.session_state.chart_path, "rb") as f:
-        st.download_button(
-            label="⬇️ Download chart",
-            data=f,
-            file_name=f"glasgow_{plot_type.lower()}.png",
-            mime="image/png",
-        )

scripts/glasgow_horizon.py

@@ -19,7 +19,8 @@
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 """
-import os
+
+import io
 from typing import Optional
 
 from datetime import datetime
@@ -29,25 +30,22 @@
 from starplot.styles import PlotStyle, extensions
 
 def make_horizon_plot(
-    output_path: str = "images/glasgow_horizon.png",
     dt: Optional[datetime] = None,
-    mag_limit: int = 5) -> str:
+    mag_limit: int = 5,
+    resolution: int = 1600) -> bytes:
     """
-    Generate a horizon star ploy
+    Generate a horizon star plot.
 
     Args:
-    - output_path: The path the image will be exported to.
     - dt: The Datetime object representing the desired time for
     the star plot
     - mag_limit: The magitude limit for stars displayed on
     the star plot.
+    - resolution: image resolution
 
-    Returns: The path for the created image.
+    Returns: The image in bytes
     """
 
-    # Ensure images folder exists
-    os.makedirs("images", exist_ok=True)
-
     # Default: In Glasgow timezone
     if dt is None:
         tz = ZoneInfo("Europe/London")
@@ -91,7 +89,9 @@ def make_horizon_plot(
     p.constellation_labels()
     p.horizon(labels={180: "SOUTH"})
 
-    # Export image
-    p.export(output_path, padding=0.1)
+    # Export to in-memory buffer
+    buf = io.BytesIO()
+    p.export(buf, format="png", resolution=resolution)
+    buf.seek(0)
 
-    return output_path
+    return buf.getvalue()  # return PNG bytes

scripts/glasgow_zenith.py

@@ -20,7 +20,7 @@
 
 """
 
-import os
+import io
 from typing import Optional
 
 from datetime import datetime
@@ -30,25 +30,22 @@
 
 
 def make_zenith_plot(
-    output_path="images/glasgow_zenith.png",
     dt: Optional[datetime] = None,
-    mag_limit: int = 5) -> str:
+    mag_limit: int = 5,
+    resolution: int = 1600) -> bytes:
     """
-    Generate a zenith star ploy
+    Generate a zenith star plot.
 
     Args:
-    - output_path: The path the image will be exported to.
     - dt: The Datetime object representing the desired time for
     the star plot
     - mag_limit: The magitude limit for stars displayed on
     the star plot.
+    - resolution: image resolution
 
-    Returns: The path for the created image.
+    Returns: The image in bytes
     """
 
-    # Ensure images folder exists
-    os.makedirs("images", exist_ok=True)
-
     # Default: now in Glasgow timezone
     if dt is None:
         tz = ZoneInfo("Europe/London")
@@ -81,8 +78,10 @@ def make_zenith_plot(
     p.horizon()
     p.constellation_labels()
 
-    # Export image
-    p.export(output_path, transparent=False)
+    # Export to in-memory buffer
+    buf = io.BytesIO()
+    p.export(buf, format="png", resolution=resolution)
+    buf.seek(0)
 
-    return output_path
+    return buf.getvalue()