Defer imports to improve startup speed

Author: hugovk

Diff for: src/tablib/core.py

@@ -8,9 +8,6 @@
     :license: MIT, see LICENSE for more details.
 """
 
-from copy import copy
-from operator import itemgetter
-
 from .exceptions import (
     HeadersNeeded,
     InvalidDatasetIndex,
@@ -638,6 +635,8 @@ def filter(self, tag):
         """Returns a new instance of the :class:`Dataset`, excluding any rows
         that do not contain the given :ref:`tags <tags>`.
         """
+        import copy
+
         _dset = copy(self)
         _dset._data = [row for row in _dset._data if row.has_tag(tag)]
 
@@ -651,6 +650,7 @@ def sort(self, col, reverse=False):
         Returns a new :class:`Dataset` instance where columns have been
         sorted.
         """
+        from operator import itemgetter
 
         if isinstance(col, str):
 
@@ -745,6 +745,8 @@ def stack(self, other):
             raise InvalidDimensions
 
         # Copy the source data
+        from copy import copy
+
         _dset = copy(self)
 
         rows_to_stack = [row for row in _dset._data]

Diff for: src/tablib/formats/_csv.py

@@ -1,7 +1,6 @@
 """ Tablib - *SV Support.
 """
 
-import csv
 from io import StringIO
 
 
@@ -14,6 +13,8 @@ class CSVFormat:
     @classmethod
     def export_stream_set(cls, dataset, **kwargs):
         """Returns CSV representation of Dataset as file-like."""
+        import csv
+
         stream = StringIO()
 
         kwargs.setdefault('delimiter', cls.DEFAULT_DELIMITER)
@@ -35,6 +36,7 @@ def export_set(cls, dataset, **kwargs):
     @classmethod
     def import_set(cls, dset, in_stream, headers=True, skip_lines=0, **kwargs):
         """Returns dataset from CSV stream."""
+        import csv
 
         dset.wipe()
 
@@ -54,6 +56,8 @@ def import_set(cls, dset, in_stream, headers=True, skip_lines=0, **kwargs):
     @classmethod
     def detect(cls, stream, delimiter=None):
         """Returns True if given stream is valid CSV."""
+        import csv
+
         try:
             csv.Sniffer().sniff(stream.read(2048), delimiters=delimiter or cls.DEFAULT_DELIMITER)
             return True

Diff for: src/tablib/formats/_json.py

@@ -1,13 +1,12 @@
 """ Tablib - JSON Support
 """
-import decimal
-import json
-from uuid import UUID
-
 import tablib
 
 
 def serialize_objects_handler(obj):
+    import decimal
+    from uuid import UUID
+
     if isinstance(obj, (decimal.Decimal, UUID)):
         return str(obj)
     elif hasattr(obj, 'isoformat'):
@@ -23,27 +22,33 @@ class JSONFormat:
     @classmethod
     def export_set(cls, dataset):
         """Returns JSON representation of Dataset."""
+        import json
+
         return json.dumps(
             dataset.dict, default=serialize_objects_handler, ensure_ascii=False
         )
 
     @classmethod
     def export_book(cls, databook):
         """Returns JSON representation of Databook."""
+        import json
+
         return json.dumps(
             databook._package(), default=serialize_objects_handler, ensure_ascii=False
         )
 
     @classmethod
     def import_set(cls, dset, in_stream):
         """Returns dataset from JSON stream."""
+        import json
 
         dset.wipe()
         dset.dict = json.load(in_stream)
 
     @classmethod
     def import_book(cls, dbook, in_stream):
         """Returns databook from JSON stream."""
+        import json
 
         dbook.wipe()
         for sheet in json.load(in_stream):
@@ -55,6 +60,8 @@ def import_book(cls, dbook, in_stream):
     @classmethod
     def detect(cls, stream):
         """Returns True if given stream is valid JSON."""
+        import json
+
         try:
             json.load(stream)
             return True