We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Add an environment variable to skip nltk.download()

Add an environment variable to skip nltk.download()


--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `deeppavlov/models/__init__.py`
Content:
```
1 # Copyright 2017 Neural Networks and Deep Learning lab, MIPT
2 #
3 # Licensed under the Apache License, Version 2.0 (the "License");
4 # you may not use this file except in compliance with the License.
5 # You may obtain a copy of the License at
6 #
7 #     http://www.apache.org/licenses/LICENSE-2.0
8 #
9 # Unless required by applicable law or agreed to in writing, software
10 # distributed under the License is distributed on an "AS IS" BASIS,
11 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 # See the License for the specific language governing permissions and
13 # limitations under the License.
14 
15 import nltk
16 
17 from deeppavlov.core.common.prints import RedirectedPrints
18 
19 
20 with RedirectedPrints():
21     nltk.download('punkt')
22     nltk.download('stopwords')
23     nltk.download('perluniprops')
24     nltk.download('nonbreaking_prefixes')
25
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/deeppavlov/models/__init__.py b/deeppavlov/models/__init__.py
--- a/deeppavlov/models/__init__.py
+++ b/deeppavlov/models/__init__.py
@@ -12,13 +12,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import os
 import nltk
 
 from deeppavlov.core.common.prints import RedirectedPrints
 
-
-with RedirectedPrints():
-    nltk.download('punkt')
-    nltk.download('stopwords')
-    nltk.download('perluniprops')
-    nltk.download('nonbreaking_prefixes')
+if not os.environ.get('DP_SKIP_NLTK_DOWNLOAD'):
+    with RedirectedPrints():
+        nltk.download('punkt')
+        nltk.download('stopwords')
+        nltk.download('perluniprops')
+        nltk.download('nonbreaking_prefixes')

{"golden_diff": "diff --git a/deeppavlov/models/__init__.py b/deeppavlov/models/__init__.py\n--- a/deeppavlov/models/__init__.py\n+++ b/deeppavlov/models/__init__.py\n@@ -12,13 +12,14 @@\n # See the License for the specific language governing permissions and\n # limitations under the License.\n \n+import os\n import nltk\n \n from deeppavlov.core.common.prints import RedirectedPrints\n \n-\n-with RedirectedPrints():\n-    nltk.download('punkt')\n-    nltk.download('stopwords')\n-    nltk.download('perluniprops')\n-    nltk.download('nonbreaking_prefixes')\n+if not os.environ.get('DP_SKIP_NLTK_DOWNLOAD'):\n+    with RedirectedPrints():\n+        nltk.download('punkt')\n+        nltk.download('stopwords')\n+        nltk.download('perluniprops')\n+        nltk.download('nonbreaking_prefixes')\n", "issue": "Add an environment variable to skip nltk.download()\n\nAdd an environment variable to skip nltk.download()\n\n", "before_files": [{"content": "# Copyright 2017 Neural Networks and Deep Learning lab, MIPT\n#\n# Licensed under the Apache License, Version 2.0 (the \"License\");\n# you may not use this file except in compliance with the License.\n# You may obtain a copy of the License at\n#\n#     http://www.apache.org/licenses/LICENSE-2.0\n#\n# Unless required by applicable law or agreed to in writing, software\n# distributed under the License is distributed on an \"AS IS\" BASIS,\n# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\n# See the License for the specific language governing permissions and\n# limitations under the License.\n\nimport nltk\n\nfrom deeppavlov.core.common.prints import RedirectedPrints\n\n\nwith RedirectedPrints():\n    nltk.download('punkt')\n    nltk.download('stopwords')\n    nltk.download('perluniprops')\n    nltk.download('nonbreaking_prefixes')\n", "path": "deeppavlov/models/__init__.py"}], "after_files": [{"content": "# Copyright 2017 Neural Networks and Deep Learning lab, MIPT\n#\n# Licensed under the Apache License, Version 2.0 (the \"License\");\n# you may not use this file except in compliance with the License.\n# You may obtain a copy of the License at\n#\n#     http://www.apache.org/licenses/LICENSE-2.0\n#\n# Unless required by applicable law or agreed to in writing, software\n# distributed under the License is distributed on an \"AS IS\" BASIS,\n# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\n# See the License for the specific language governing permissions and\n# limitations under the License.\n\nimport os\nimport nltk\n\nfrom deeppavlov.core.common.prints import RedirectedPrints\n\nif not os.environ.get('DP_SKIP_NLTK_DOWNLOAD'):\n    with RedirectedPrints():\n        nltk.download('punkt')\n        nltk.download('stopwords')\n        nltk.download('perluniprops')\n        nltk.download('nonbreaking_prefixes')\n", "path": "deeppavlov/models/__init__.py"}]}