enable read from python

python/paddle/fluid/__init__.py

@@ -123,7 +123,7 @@ def __bootstrap__():
     read_env_flags = [
         'use_pinned_memory', 'check_nan_inf', 'benchmark', 'warpctc_dir',
         'eager_delete_scope', 'use_mkldnn', 'initial_cpu_memory_in_mb',
-        'init_allocated_mem', 'free_idle_memory'
+        'init_allocated_mem', 'free_idle_memory', 'paddle_num_threads'
     ]
     if core.is_compiled_with_dist():
         read_env_flags.append('rpc_deadline')