[Python] Overhaul "Setup tracing" > "Custom instrumentation" (#11341)

- Add documentation for manual span creation (without context manager)
- Clean up code snippets
- Made all callout boxes the same color, to make page more calm.

---------

Co-authored-by: Ivana Kellyer <[email protected]>
Co-authored-by: Daniel Szoke <[email protected]>

Author: 3 people

docs/platforms/python/tracing/instrumentation/custom-instrumentation/index.mdx

@@ -9,11 +9,11 @@ The Sentry SDK for Python does a very good job of auto instrumenting your applic
 
 Adding transactions will allow you to instrument and capture certain regions of your code.
 
-<Note>
+<Alert level="info">
 
 If you're using one of Sentry's SDK integrations, transactions will be created for you automatically.
 
-</Note>
+</Alert>
 
 The following example creates a transaction for an expensive operation (in this case, `eat_pizza`), and then sends the result to Sentry:
 
@@ -35,8 +35,9 @@ The [API reference](https://getsentry.github.io/sentry-python/api.html#sentry_sd
 
 If you want to have more fine-grained performance monitoring, you can add child spans to your transaction, which can be done by either:
 
-- Using a context manager or
-- Using a decorator, (this works on sync and `async` functions)
+- Using a context manager
+- Using a decorator (this works on sync and async functions)
+- Manually starting and finishing a span
 
 Calling a `sentry_sdk.start_span()` will find the current active transaction and attach the span to it.
 
@@ -53,7 +54,6 @@ def eat_pizza(pizza):
         while pizza.slices > 0:
             with sentry_sdk.start_span(description="Eat Slice"):
                 eat_slice(pizza.slices.pop())
-
 ```
 
 ### Using a Decorator
@@ -69,15 +69,32 @@ def eat_pizza(pizza):
     with sentry_sdk.start_transaction(op="task", name="Eat Pizza"):
         while pizza.slices > 0:
             eat_slice(pizza.slices.pop())
-
 ```
 
-<Alert title="Static & Class Methods" level="warning">
+<Alert title="Static & Class Methods" level="info">
 
 When tracing a static or class method, you **must** add the `@sentry_sdk.trace` decorator **after** the `@staticmethod` or `@classmethod` decorator (i.e., **closer** to the function definition). Otherwise, your function will break!
 
 </Alert>
 
+### Manually Starting and Finishing a Span
+
+```python
+import sentry_sdk
+
+def eat_slice(slice):
+    ...
+
+def eat_pizza(pizza):
+    with sentry_sdk.start_transaction(op="task", name="Eat Pizza"):
+        while pizza.slices > 0:
+            span = sentry_sdk.start_span(description="Eat Slice")
+            eat_slice(pizza.slices.pop())
+            span.finish()
+```
+
+When you create your span manually, make sure to call `span.finish()` after the block of code you want to wrap in a span to finish the span. If you do not finish the span it will not be sent to Sentry.
+
 ## Nested Spans
 
 Spans can be nested to form a span tree. If you'd like to learn more, read our [distributed tracing](/product/sentry-basics/tracing/distributed-tracing/) documentation.
@@ -90,16 +107,10 @@ import sentry_sdk
 def chew():
     ...
 
-def swallow():
-    ...
-
 def eat_slice(slice):
     with sentry_sdk.start_span(description="Eat Slice"):
         with sentry_sdk.start_span(description="Chew"):
             chew()
-        with sentry_sdk.start_span(description="Swallow"):
-            swallow()
-
 ```
 
 ### Using a Decorator
@@ -112,15 +123,32 @@ def chew():
     ...
 
 @sentry_sdk.trace
-def swallow():
+def eat_slice(slice):
+    chew()
+```
+
+### Manually
+
+```python
+import sentry_sdk
+
+def chew():
     ...
 
-@sentry_sdk.trace
 def eat_slice(slice):
+    parent_span = sentry_sdk.start_span(description="Eat Slice")
+
+    child_span = parent_span.start_child(description="Chew")
     chew()
-    swallow()
+    child_span.finish()
+
+    parent_span.finish()
 ```
 
+The parameters of `start_span()` and `start_child()` are the same. See the [API reference](https://getsentry.github.io/sentry-python/api.html#sentry_sdk.api.start_span) for more details.
+
+When you create your span manually, make sure to call `span.finish()` after the block of code you want to wrap in a span to finish the span. If you do not finish the span it will not be sent to Sentry.
+
 ## Define Span Creation in a Central Place
 
 To avoid having custom performance instrumentation code scattered all over your code base, pass a parameter <PlatformIdentifier name="functions-to-trace" /> to your `sentry_sdk.init()` call.
@@ -145,21 +173,21 @@ sentry_sdk.init(
 
 Now, whenever a function specified in `functions_to_trace` will be executed, a span will be created and attached as a child to the currently running span.
 
-<Alert level="warning" title="Important">
+<Alert title="Important" level="info">
 
 To enable performance monitoring for the functions specified in `functions_to_trace`, the SDK needs to load the function modules. Be aware, there may be code being executed in modules during module loading. To avoid this, use the method described above to trace your functions.
 
 </Alert>
 
 ## Accessing the Current Transaction
 
-To change data in an already ongoing transaction, use `Hub.current.scope.transaction`. This property will return a transaction if there's one running, otherwise it will return `None`.
+The `sentry_sdk.get_current_scope().transaction` property returns the active transaction or `None` if no transaction is active. You can use this property to modify data on the transaction.
 
 ```python
 import sentry_sdk
 
 def eat_pizza(pizza):
-    transaction = sentry_sdk.Hub.current.scope.transaction
+    transaction = sentry_sdk.get_current_scope().transaction
 
     if transaction is not None:
         transaction.set_tag("num_of_slices", len(pizza.slices))
@@ -170,7 +198,7 @@ def eat_pizza(pizza):
 
 ## Accessing the Current Span
 
-To change data in the current span, use `sentry_sdk.Hub.current.scope.span`. This property will return a span if there's one running, otherwise it will return `None`.
+To change data in the current span, use ` sentry_sdk.get_current_span()`. This function will return a span if there's one running, otherwise it will return `None`.
 
 In this example, we'll set a tag in the span created by the `@sentry_sdk.trace` decorator.
 
@@ -179,10 +207,8 @@ import sentry_sdk
 
 @sentry_sdk.trace
 def eat_slice(slice):
-    span = sentry_sdk.Hub.current.scope.span
+    span = sentry_sdk.get_current_span()
 
     if span is not None:
         span.set_tag("slice_id", slice.id)
-
-    ...
 ```