Remove Pexpect Dependency (#3667)

Resolves #3664

Next PR will be to clean up CI to catch this earlier. Triaging this, it
looks like it wasn't caught because pexpect is a `poetry` dependency.

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

langchain/utilities/bash.py

@@ -1,10 +1,29 @@
 """Wrapper around subprocess to run commands."""
+from __future__ import annotations
+
+import platform
 import re
 import subprocess
-from typing import List, Union
+from typing import TYPE_CHECKING, List, Union
 from uuid import uuid4
 
-import pexpect
+if TYPE_CHECKING:
+    import pexpect
+
+
+def _lazy_import_pexpect() -> pexpect:
+    """Import pexpect only when needed."""
+    if platform.system() == "Windows":
+        raise ValueError("Persistent bash processes are not yet supported on Windows.")
+    try:
+        import pexpect
+
+    except ImportError:
+        raise ImportError(
+            "pexpect required for persistent bash processes."
+            " To install, run `pip install pexpect`."
+        )
+    return pexpect
 
 
 class BashProcess:
@@ -28,6 +47,8 @@ class BashProcess:
     @staticmethod
     def _initialize_persistent_process(prompt: str) -> pexpect.spawn:
         # Start bash in a clean environment
+        # Doesn't work on windows
+        pexpect = _lazy_import_pexpect()
         process = pexpect.spawn(
             "env", ["-i", "bash", "--norc", "--noprofile"], encoding="utf-8"
         )
@@ -75,6 +96,7 @@ class BashProcess:
 
     def _run_persistent(self, command: str) -> str:
         """Run commands and return final output."""
+        pexpect = _lazy_import_pexpect()
         if self.process is None:
             raise ValueError("Process not initialized")
         self.process.sendline(command)

pyproject.toml

@@ -73,6 +73,7 @@ duckduckgo-search = {version="^2.8.6", optional=true}
 azure-cosmos = {version="^4.4.0b1", optional=true}
 lark = {version="^1.1.5", optional=true}
 lancedb = {version = "^0.1", optional = true}
+pexpect = {version = "^4.8.0", optional = true}
 
 [tool.poetry.group.docs.dependencies]
 autodoc_pydantic = "^1.8.0"
@@ -150,7 +151,7 @@ openai = ["openai"]
 cohere = ["cohere"]
 embeddings = ["sentence-transformers"]
 azure = ["azure-identity", "azure-cosmos", "openai", "azure-core"]
-all = ["anthropic", "cohere", "openai", "nlpcloud", "huggingface_hub", "jina", "manifest-ml", "elasticsearch", "opensearch-py", "google-search-results", "faiss-cpu", "sentence-transformers", "transformers", "spacy", "nltk", "wikipedia", "beautifulsoup4", "tiktoken", "torch", "jinja2", "pinecone-client", "pinecone-text", "weaviate-client", "redis", "google-api-python-client", "wolframalpha", "qdrant-client", "tensorflow-text", "pypdf", "networkx", "nomic", "aleph-alpha-client", "deeplake", "pgvector", "psycopg2-binary", "boto3", "pyowm", "pytesseract", "html2text", "atlassian-python-api", "gptcache", "duckduckgo-search", "arxiv", "azure-identity", "clickhouse-connect", "azure-cosmos", "lancedb", "lark"]
+all = ["anthropic", "cohere", "openai", "nlpcloud", "huggingface_hub", "jina", "manifest-ml", "elasticsearch", "opensearch-py", "google-search-results", "faiss-cpu", "sentence-transformers", "transformers", "spacy", "nltk", "wikipedia", "beautifulsoup4", "tiktoken", "torch", "jinja2", "pinecone-client", "pinecone-text", "weaviate-client", "redis", "google-api-python-client", "wolframalpha", "qdrant-client", "tensorflow-text", "pypdf", "networkx", "nomic", "aleph-alpha-client", "deeplake", "pgvector", "psycopg2-binary", "boto3", "pyowm", "pytesseract", "html2text", "atlassian-python-api", "gptcache", "duckduckgo-search", "arxiv", "azure-identity", "clickhouse-connect", "azure-cosmos", "lancedb", "lark", "pexpect"]
 
 [tool.ruff]
 select = [