build: make dependency on Click optional

CHANGELOG.rst

@@ -17,6 +17,11 @@ Added
 - Added BIP32 master extended private key to test vectors.
 - Added support for extendable backup flag.
 
+Changed
+~~~~~~~
+- Dependency on `click` is now optional. In order to use the CLI tool, install the `cli`
+  extra. For example, `pip install shamir-mnemonic[cli]`.
+
 Removed
 ~~~~~~~
 

README.rst

@@ -35,11 +35,11 @@ not be used for handling sensitive secrets**.
 Installation
 ------------
 
-With pip from GitHub:
+With pip from PyPI:
 
 .. code-block:: console
 
-    $ pip3 install shamir-mnemonic
+    $ pip3 install shamir-mnemonic[cli]  # for CLI tool
 
 From local checkout for development:
 

pyproject.toml

@@ -11,15 +11,18 @@ readme = [
 
 [tool.poetry.dependencies]
 python = ">=3.6,<4.0"
-click = ">=7,<9"
 dataclasses = { version = "*", python = "<=3.6" }
+click = { version = ">=7,<9", optional = true }
 
 [tool.poetry.group.dev.dependencies]
 bip32utils = "^0.3.post4"
 pytest = "*"
 black = ">=20"
 isort = "^5"
 
+[tool.poetry.extras]
+cli = ["click"]
+
 [tool.poetry.scripts]
 shamir = "shamir_mnemonic.cli:cli"
 

shamir_mnemonic/cli.py

@@ -2,8 +2,14 @@
 import sys
 from typing import Sequence, Tuple
 
-import click
-from click import style
+try:
+    import click
+    from click import style
+
+except ImportError:
+    print("Required dependencies are missing. Install them with:")
+    print("  pip install shamir_mnemonic[cli]")
+    sys.exit(1)
 
 from .recovery import RecoveryState
 from .shamir import generate_mnemonics