Merge pull request #93 from YuanYuYuan/fix/python-example

fix: wrap zenoh-python sessions in context manager

Author: wyfo

content/docs/getting-started/first-app.md

@@ -10,10 +10,10 @@ Let us take a step-by-step approach in putting together your first Zenoh applica
 As the first step, let us see how we get some data from a temperature sensor in our kitchen.
 Then we see how we can route this data to store and perform some analytics.
 
-Before cranking some code, let's define some terminology. 
+Before cranking some code, let's define some terminology.
 
 <b>Zenoh</b> deals with <i>keys/values</i> where each key is a <i>path</i> and is associated to a <i>value</i>. A key looks like just a Unix file system path, such as ```myhome/kitchen/temp```. The value can be defined with different
-encodings (string, JSON, raw bytes buffer...). 
+encodings (string, JSON, raw bytes buffer...).
 <!-- To query the values stored by Zenoh, we use <i>selectors</i>. As the name suggest, a <i>selector</i> can use wildcards, such as <b>*</b> and <b>**</b> to represent a set of paths, such as, ```myhome/*/temp```. -->
 
 Let's get started!
@@ -37,15 +37,15 @@ def read_temp():
     return random.randint(15, 30)
 
 if __name__ == "__main__":
-    session = zenoh.open(zenoh.Config())
-    key = 'myhome/kitchen/temp'
-    pub = session.declare_publisher(key)
-    while True:
-        t = read_temp()
-        buf = f"{t}"
-        print(f"Putting Data ('{key}': '{buf}')...")
-        pub.put(buf)
-        time.sleep(1)
+    with zenoh.open(zenoh.Config()) as session:
+        key = 'myhome/kitchen/temp'
+        pub = session.declare_publisher(key)
+        while True:
+            t = read_temp()
+            buf = f"{t}"
+            print(f"Putting Data ('{key}': '{buf}')...")
+            pub.put(buf)
+            time.sleep(1)
 ```
 
 Now we need a subscriber, `z_subscriber.py` that can receive the measurements:
@@ -55,19 +55,19 @@ import zenoh, time
 
 def listener(sample):
     print(f"Received {sample.kind} ('{sample.key_expr}': '{sample.payload.to_string()}')")
-    
+
 if __name__ == "__main__":
-    session = zenoh.open(zenoh.Config())
-    sub = session.declare_subscriber('myhome/kitchen/temp', listener)
-    time.sleep(60)
+    with zenoh.open(zenoh.Config()) as session:
+        sub = session.declare_subscriber('myhome/kitchen/temp', listener)
+        time.sleep(60)
 ```
 
 Start the subscriber:
 ```bash
 python3 z_subscriber.py
 ```
 The subscriber waits for an update on `myhome/kitchen/temp`.
- 
+
 Now start `z_sensor.py` as follows
 ```bash
 python3 z_sensor.py
@@ -78,7 +78,7 @@ You can see the values produced by the sensor being consumed by the subscriber.
 ## Store and Query in Zenoh
 
 As the next step, let's see how the value generated by a publisher can be stored in Zenoh.
-For this, we use [Zenoh router](../installation) (`zenohd`). 
+For this, we use [Zenoh router](../installation) (`zenohd`).
 By default, a Zenoh router starts without any storage. In order to store the temperature, we need to configure one.
 Create a `zenoh-myhome.json5` configuration file for Zenoh with this content:
 ```json5
@@ -107,24 +107,23 @@ Create a `zenoh-myhome.json5` configuration file for Zenoh with this content:
 zenohd -c zenoh-myhome.json5
 ```
 
-Now the data generated by our temperature sensor is stored in memory. 
+Now the data generated by our temperature sensor is stored in memory.
 We can retrieve the latest temperature value stored in Zenoh:
 
 ```python
 import zenoh
 
 if __name__ == "__main__":
-    session = zenoh.open()
-    replies = session.get('myhome/kitchen/temp')
-    for reply in replies:
-        try:
-            print("Received ('{}': '{}')"
-                .format(reply.ok.key_expr, reply.ok.payload.to_string()))
-        except:
-            print("Received (ERROR: '{}')"
-                .format(reply.err.payload.to_string()))
-
-session.close()
+    with zenoh.open(zenoh.Config()) as session:
+      replies = session.get('myhome/kitchen/temp')
+      for reply in replies:
+          try:
+              print("Received ('{}': '{}')"
+                  .format(reply.ok.key_expr, reply.ok.payload.to_string()))
+          except:
+              print("Received (ERROR: '{}')"
+                  .format(reply.err.payload.to_string()))
+
 ```
 ## Other examples