Reimplement .map logic making Node immutable

ffmpeg/_ffmpeg.py

@@ -83,9 +83,7 @@ def map(*streams):
     if not tail:
         return head
 
-    head.node._add_streams(tail)
-
-    return head
+    return OutputNode(head.node, tail).stream()
 
 
 __all__ = [

ffmpeg/nodes.py

@@ -1,9 +1,12 @@
 from __future__ import unicode_literals
 
+import warnings
+
 from .dag import KwargReprNode
 from ._utils import escape_chars, get_hash_int
 from builtins import object
-import os
+import os, sys
+import inspect
 
 
 def _is_of_types(obj, types):
@@ -19,6 +22,13 @@ def _get_types_str(types):
     return ', '.join(['{}.{}'.format(x.__module__, x.__name__) for x in types])
 
 
+def _get_arg_count(callable):
+    if sys.version_info.major >= 3:
+        return len(inspect.getfullargspec(callable).args)
+    else:
+        return len(inspect.getargspec(callable).args)
+
+
 class Stream(object):
     """Represents the outgoing edge of an upstream node; may be used to create more downstream nodes."""
 
@@ -30,6 +40,7 @@ class Stream(object):
         self.label = upstream_label
         self.selector = upstream_selector
 
+
     def __hash__(self):
         return get_hash_int([hash(self.node), hash(self.label)])
 
@@ -85,6 +96,22 @@ def get_stream_spec_nodes(stream_spec):
 class Node(KwargReprNode):
     """Node base"""
 
+    @property
+    def min_inputs(self):
+        return self.__min_inputs
+
+    @property
+    def max_inputs(self):
+        return self.__max_inputs
+
+    @property
+    def incoming_stream_types(self):
+        return self.__incoming_stream_types
+
+    @property
+    def outgoing_stream_type(self):
+        return self.__outgoing_stream_type
+
     @classmethod
     def __check_input_len(cls, stream_map, min_inputs, max_inputs):
         if min_inputs is not None and len(stream_map) < min_inputs:
@@ -106,19 +133,85 @@ class Node(KwargReprNode):
             incoming_edge_map[downstream_label] = (upstream.node, upstream.label, upstream.selector)
         return incoming_edge_map
 
-    def __init__(self, stream_spec, name, incoming_stream_types, outgoing_stream_type, min_inputs, max_inputs, args=[],
-                 kwargs={}):
+    def __init_fromscratch__(self, stream_spec, name, incoming_stream_types, outgoing_stream_type, min_inputs,
+                             max_inputs, args=[],
+                             kwargs={}):
         stream_map = get_stream_map(stream_spec)
         self.__check_input_len(stream_map, min_inputs, max_inputs)
         self.__check_input_types(stream_map, incoming_stream_types)
         incoming_edge_map = self.__get_incoming_edge_map(stream_map)
+
         super(Node, self).__init__(incoming_edge_map, name, args, kwargs)
         self.__outgoing_stream_type = outgoing_stream_type
-
         self.__incoming_stream_types = incoming_stream_types
         self.__min_inputs = min_inputs
         self.__max_inputs = max_inputs
 
+    def __init_fromnode__(self, old_node, stream_spec):
+        # Make sure old node and new node are of the same type
+        if type(self) != type(old_node):
+            raise ValueError("'old_node' should be of type {}".format(self.__class__.__name__))
+
+        # Copy needed data from old node
+        name = old_node.name
+        incoming_stream_types = old_node.incoming_stream_types
+        outgoing_stream_type = old_node.outgoing_stream_type
+        min_inputs = old_node.min_inputs
+        max_inputs = old_node.max_inputs
+        prev_edges = old_node.incoming_edge_map.values()
+        args = old_node.args
+        kwargs = old_node.kwargs
+
+        # Check new stream spec - the old spec should have already been checked
+        new_stream_map = get_stream_map(stream_spec)
+        self.__check_input_types(new_stream_map, incoming_stream_types)
+
+        # Generate new edge map
+        new_inc_edge_map = self.__get_incoming_edge_map(new_stream_map)
+        new_edges = new_inc_edge_map.values()
+
+        # Rename all edges
+        new_edge_map = dict(enumerate(list(prev_edges) + list(new_edges)))
+
+        # Check new length
+        self.__check_input_len(new_edge_map, min_inputs, max_inputs)
+
+        super(Node, self).__init__(new_edge_map, name, args, kwargs)
+        self.__outgoing_stream_type = outgoing_stream_type
+        self.__incoming_stream_types = incoming_stream_types
+        self.__min_inputs = min_inputs
+        self.__max_inputs = max_inputs
+
+    # noinspection PyMissingConstructor
+    def __init__(self, *args, **kwargs):
+        """
+        If called with the following arguments, the new Node is created from scratch:
+        - stream_spec, name, incoming_stream_types, outgoing_stream_type, min_inputs, max_inputs, args=[], kwargs={}
+
+        If called with the following arguments, the new node is a copy of `old_node` that includes the additional
+        `stream_spec`:
+        - old_node, stream_spec
+        """
+        # Python doesn't support constructor overloading. This hacky code detects how we want to construct the object
+        # based on the number of arguments and the type of the first argument, then calls the appropriate constructor
+        # helper method
+
+        # "1+" is for `self`
+        argc = 1 + len(args) + len(kwargs)
+
+        first_arg = "old_node" in kwargs and kwargs["old_node"] or args[0]
+
+        if argc == _get_arg_count(self.__init_fromnode__) and type(first_arg) == type(self):
+            self.__init_fromnode__(*args, **kwargs)
+        else:
+            if isinstance(first_arg, Node):
+                raise ValueError(
+                    "{}.__init__() received an instance of {} as the first argument. If you want to create a "
+                    "copy of an existing node, the types must match and you must provide an additional stream_spec."
+                    .format(self.__class__.__name__, first_arg.__class__.__name__)
+                )
+            self.__init_fromscratch__(*args, **kwargs)
+
     def stream(self, label=None, select=None):
         """Create an outgoing stream originating from this node.
 
@@ -136,31 +229,6 @@ class Node(KwargReprNode):
         else:
             return self.stream(label=item)
 
-    def _add_streams(self, stream_spec):
-        """Attach additional streams after the Node is initialized.
-        """
-        # Back up previous edges
-        prev_edges = self.incoming_edge_map.values()
-
-        # Check new edges
-        new_stream_map = get_stream_map(stream_spec)
-        self.__check_input_types(new_stream_map, self.__incoming_stream_types)
-
-        # Generate new edge map
-        new_inc_edge_map = self.__get_incoming_edge_map(new_stream_map)
-        new_edges = new_inc_edge_map.values()
-
-        # Rename all edges
-        new_edge_map = dict(enumerate(list(prev_edges) + list(new_edges)))
-
-        # Check new length
-        self.__check_input_len(new_edge_map, self.__min_inputs, self.__max_inputs)
-
-        # Overwrite old map (exploiting the fact that dict is mutable; incoming_edge_map is a read-only property)
-        if None in self.incoming_edge_map:
-            self.incoming_edge_map.pop(None)
-        self.incoming_edge_map.update(new_edge_map)
-
 
 class FilterableStream(Stream):
     def __init__(self, upstream_node, upstream_label, upstream_selector=None):
@@ -168,11 +236,12 @@ class FilterableStream(Stream):
                                                upstream_selector)
 
 
+# noinspection PyMethodOverriding
 class InputNode(Node):
     """InputNode type"""
 
-    def __init__(self, name, args=[], kwargs={}):
-        super(InputNode, self).__init__(
+    def __init_fromscratch__(self, name, args=[], kwargs={}):
+        super(InputNode, self).__init_fromscratch__(
             stream_spec=None,
             name=name,
             incoming_stream_types={},
@@ -183,14 +252,18 @@ class InputNode(Node):
             kwargs=kwargs
         )
 
+    def __init_fromnode__(self, old_node, stream_spec):
+        raise TypeError("{} can't be constructed from an existing node".format(self.__class__.__name__))
+
     @property
     def short_repr(self):
         return os.path.basename(self.kwargs['filename'])
 
 
+# noinspection PyMethodOverriding
 class FilterNode(Node):
-    def __init__(self, stream_spec, name, max_inputs=1, args=[], kwargs={}):
-        super(FilterNode, self).__init__(
+    def __init_fromscratch__(self, stream_spec, name, max_inputs=1, args=[], kwargs={}):
+        super(FilterNode, self).__init_fromscratch__(
             stream_spec=stream_spec,
             name=name,
             incoming_stream_types={FilterableStream},
@@ -227,9 +300,10 @@ class FilterNode(Node):
         return escape_chars(params_text, '\\\'[],;')
 
 
+# noinspection PyMethodOverriding
 class OutputNode(Node):
-    def __init__(self, stream, name, args=[], kwargs={}):
-        super(OutputNode, self).__init__(
+    def __init_fromscratch__(self, stream, name, args=[], kwargs={}):
+        super(OutputNode, self).__init_fromscratch__(
             stream_spec=stream,
             name=name,
             incoming_stream_types={FilterableStream},
@@ -251,9 +325,10 @@ class OutputStream(Stream):
                                            upstream_selector=upstream_selector)
 
 
+# noinspection PyMethodOverriding
 class MergeOutputsNode(Node):
-    def __init__(self, streams, name):
-        super(MergeOutputsNode, self).__init__(
+    def __init_fromscratch__(self, streams, name):
+        super(MergeOutputsNode, self).__init_fromscratch__(
             stream_spec=streams,
             name=name,
             incoming_stream_types={OutputStream},
@@ -263,9 +338,10 @@ class MergeOutputsNode(Node):
         )
 
 
+# noinspection PyMethodOverriding
 class GlobalNode(Node):
-    def __init__(self, stream, name, args=[], kwargs={}):
-        super(GlobalNode, self).__init__(
+    def __init_fromscratch__(self, stream, name, args=[], kwargs={}):
+        super(GlobalNode, self).__init_fromscratch__(
             stream_spec=stream,
             name=name,
             incoming_stream_types={OutputStream},
@@ -276,6 +352,9 @@ class GlobalNode(Node):
             kwargs=kwargs
         )
 
+    def __init_fromnode__(self, old_node, stream_spec):
+        raise TypeError("{} can't be constructed from an existing node".format(self.__class__.__name__))
+
 
 def stream_operator(stream_classes={Stream}, name=None):
     def decorator(func):

ffmpeg/tests/test_ffmpeg.py

@@ -166,11 +166,12 @@ def test_map_same_effect_as_output():
     i1 = ffmpeg.input(TEST_INPUT_FILE1)
     i2 = ffmpeg.input(TEST_OVERLAY_FILE)
 
-    o_map = i1.output(TEST_OUTPUT_FILE1)
-    o_map.map(i2)
+    _o_map = i1.output(TEST_OUTPUT_FILE1)
+    o_map = _o_map.map(i2)
 
     o_nomap = ffmpeg.output(i1, i2, TEST_OUTPUT_FILE1)
 
+    assert id(o_map) != id(_o_map)  # Checks immutability
     assert o_map.node.incoming_edge_map == o_nomap.node.incoming_edge_map
     assert o_map.get_args() == o_nomap.get_args() == ['-i', TEST_INPUT_FILE1,
                                                       '-i', TEST_OVERLAY_FILE,