Revise python tutorial lesson 16 to make sure tutorial text and code match.
diff --git a/examples/tracing/task_switch.py b/examples/tracing/task_switch.py
index 161edfb..43a4f3f 100755
--- a/examples/tracing/task_switch.py
+++ b/examples/tracing/task_switch.py
@@ -5,29 +5,7 @@
 from bcc import BPF
 from time import sleep
 
-b = BPF(text="""
-#include <uapi/linux/ptrace.h>
-#include <linux/sched.h>
-
-struct key_t {
-  u32 prev_pid;
-  u32 curr_pid;
-};
-// map_type, key_type, leaf_type, table_name, num_entry
-BPF_HASH(stats, struct key_t, u64, 1024);
-int count_sched(struct pt_regs *ctx, struct task_struct *prev) {
-  struct key_t key = {};
-  u64 zero = 0, *val;
-
-  key.curr_pid = bpf_get_current_pid_tgid();
-  key.prev_pid = prev->pid;
-
-  // could also use `stats.increment(key);`
-  val = stats.lookup_or_init(&key, &zero);
-  (*val)++;
-  return 0;
-}
-""")
+b = BPF(src_file="task_switch.c")
 b.attach_kprobe(event="finish_task_switch", fn_name="count_sched")
 
 # generate many schedule events