diff --git a/intake/source/base.py b/intake/source/base.py
index f3abbbb..79fc62e 100644
--- a/intake/source/base.py
+++ b/intake/source/base.py
@@ -259,13 +259,26 @@ class DataSource(DictSerialiseMixin):
         return self.plot
 
     def persist(self, ttl=None, **kwargs):
-        """Save data from this source to local persistent storage"""
+        """Save data from this source to local persistent storage
+
+        Parameters
+        ----------
+        ttl: numeric, optional
+            Time to live in seconds. If provided, the original source will
+            be accessed and a new persisted version written transparently
+            when more than ``ttl`` seconds have passed since the old persisted
+            version was written.
+        kargs: passed to the _persist method on the base container.
+        """
         from ..container import container_map
         from ..container.persist import PersistStore
         import time
         if 'original_tok' in self.metadata:
             raise ValueError('Cannot persist a source taken from the persist '
                              'store')
+        if ttl is not None and not isinstance(ttl, (int, float)):
+            raise ValueError('Cannot persist using a time to live that is '
+                             f'non-numeric. User-provided ttl was {ttl}')
         method = container_map[self.container]._persist
         store = PersistStore()
         out = method(self, path=store.getdir(self), **kwargs)

persist ttl argument should check that it's an int.
I just tried to use persist for the first time and passed a file name to the `ttl` argument (don't ask me why but I kind of thought `ttl` might be a terrible abbreviation of title). Passing a string to ttl did not through an error, but when I try to call `is_persisted` on the source, I am getting a comparison failure. 

As part of this, might be nice to add to the persist docstring. 
diff --git a/intake/container/tests/test_persist.py b/intake/container/tests/test_persist.py
index d914d25..96a831f 100644
--- a/intake/container/tests/test_persist.py
+++ b/intake/container/tests/test_persist.py
@@ -44,6 +44,12 @@ def test_backtrack(temp_cache):
     assert s3 == s
 
 
+def test_persist_with_nonnumeric_ttl_raises_error(temp_cache):
+    s = TextFilesSource("*.py")
+    with pytest.raises(ValueError, match="User-provided ttl was a string"):
+        s.persist(ttl='a string')
+
+
 class DummyDataframe(DataSource):
     name = 'dummy'
     container = 'dataframe'

pip install -e .[complete]
parse_log_pytest
requirements.txt
intake-parquet zarr notebook panel==0.5.1 hvplot==0.4.0 fsspec pytest
apt-get update apt-get install -y libsnappy-dev
3.9
requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
anyio==4.9.0
appdirs==1.4.4
argon2-cffi==23.1.0
argon2-cffi-bindings==21.2.0
arrow==1.3.0
asciitree==0.3.3
asttokens==3.0.0
async-lru==2.0.5
attrs==25.3.0
babel==2.17.0
beautifulsoup4==4.13.3
bleach==6.2.0
bokeh==3.4.3
certifi==2025.1.31
cffi==1.17.1
charset-normalizer==3.4.1
click==8.1.8
cloudpickle==3.1.1
comm==0.2.2
contourpy==1.3.0
cramjam==2.9.1
dask==2024.8.0
dask-expr==1.1.10
debugpy==1.8.13
decorator==5.2.1
defusedxml==0.7.1
entrypoints==0.4
exceptiongroup==1.2.2
executing==2.2.0
fasteners==0.19
fastjsonschema==2.21.1
fastparquet==2024.11.0
fqdn==1.5.1
fsspec==2025.3.1
h11==0.14.0
holoviews==1.12.7
httpcore==1.0.7
httpx==0.28.1
hvplot==0.4.0
idna==3.10
importlib_metadata==8.6.1
iniconfig==2.1.0
-e git+https://github.com/intake/intake.git@aa83ccd41ed32f90f6bef5dbbe0e8a9e67c6d781#egg=intake
intake-parquet==0.3.0
ipykernel==6.29.5
ipython==8.18.1
isoduration==20.11.0
jedi==0.19.2
Jinja2==3.1.6
json5==0.10.0
jsonpointer==3.0.0
jsonschema==4.23.0
jsonschema-specifications==2024.10.1
jupyter-events==0.12.0
jupyter-lsp==2.2.5
jupyter_client==8.6.3
jupyter_core==5.7.2
jupyter_server==2.15.0
jupyter_server_terminals==0.5.3
jupyterlab==4.3.6
jupyterlab_pygments==0.3.0
jupyterlab_server==2.27.3
locket==1.0.0
Markdown==3.7
MarkupSafe==3.0.2
matplotlib-inline==0.1.7
mistune==3.1.3
msgpack==1.1.0
msgpack-numpy==0.4.8
nbclient==0.10.2
nbconvert==7.16.6
nbformat==5.10.4
nest-asyncio==1.6.0
networkx==3.2.1
notebook==7.3.3
notebook_shim==0.2.4
numcodecs==0.12.1
numpy==2.0.2
overrides==7.7.0
packaging==24.2
pandas==2.2.3
pandocfilters==1.5.1
panel==0.5.1
param==1.13.0
parso==0.8.4
partd==1.4.2
pexpect==4.9.0
pillow==11.1.0
platformdirs==4.3.7
pluggy==1.5.0
prometheus_client==0.21.1
prompt_toolkit==3.0.50
psutil==7.0.0
ptyprocess==0.7.0
pure_eval==0.2.3
pyarrow==19.0.1
pycparser==2.22
pyct==0.5.0
Pygments==2.19.1
pytest==8.3.5
python-dateutil==2.9.0.post0
python-json-logger==3.3.0
python-snappy==0.7.3
pytz==2025.2
pyviz_comms==3.0.4
PyYAML==6.0.2
pyzmq==26.3.0
referencing==0.36.2
requests==2.32.3
rfc3339-validator==0.1.4
rfc3986-validator==0.1.1
rpds-py==0.24.0
Send2Trash==1.8.3
six==1.17.0
sniffio==1.3.1
soupsieve==2.6
stack-data==0.6.3
terminado==0.18.1
testpath==0.3.1
tinycss2==1.4.0
tomli==2.2.1
toolz==1.0.0
tornado==6.4.2
traitlets==5.14.3
types-python-dateutil==2.9.0.20241206
typing_extensions==4.13.0
tzdata==2025.2
uri-template==1.3.0
urllib3==2.3.0
wcwidth==0.2.13
webcolors==24.11.1
webencodings==0.5.1
websocket-client==1.8.0
xyzservices==2025.1.0
zarr==2.18.2
zipp==3.21.0

name: intake
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.4.4=h6a678d5_1
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=3.0.16=h5eee18b_0
  - pip=25.0=py39h06a4308_0
  - python=3.9.21=he870216_1
  - readline=8.2=h5eee18b_0
  - setuptools=75.8.0=py39h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.45.1=py39h06a4308_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - anyio==4.9.0
      - appdirs==1.4.4
      - argon2-cffi==23.1.0
      - argon2-cffi-bindings==21.2.0
      - arrow==1.3.0
      - asciitree==0.3.3
      - asttokens==3.0.0
      - async-lru==2.0.5
      - attrs==25.3.0
      - babel==2.17.0
      - beautifulsoup4==4.13.3
      - bleach==6.2.0
      - bokeh==3.4.3
      - certifi==2025.1.31
      - cffi==1.17.1
      - charset-normalizer==3.4.1
      - click==8.1.8
      - cloudpickle==3.1.1
      - comm==0.2.2
      - contourpy==1.3.0
      - cramjam==2.9.1
      - dask==2024.8.0
      - dask-expr==1.1.10
      - debugpy==1.8.13
      - decorator==5.2.1
      - defusedxml==0.7.1
      - entrypoints==0.4
      - exceptiongroup==1.2.2
      - executing==2.2.0
      - fasteners==0.19
      - fastjsonschema==2.21.1
      - fastparquet==2024.11.0
      - fqdn==1.5.1
      - fsspec==2025.3.1
      - h11==0.14.0
      - holoviews==1.12.7
      - httpcore==1.0.7
      - httpx==0.28.1
      - hvplot==0.4.0
      - idna==3.10
      - importlib-metadata==8.6.1
      - iniconfig==2.1.0
      - intake-parquet==0.3.0
      - ipykernel==6.29.5
      - ipython==8.18.1
      - isoduration==20.11.0
      - jedi==0.19.2
      - jinja2==3.1.6
      - json5==0.10.0
      - jsonpointer==3.0.0
      - jsonschema==4.23.0
      - jsonschema-specifications==2024.10.1
      - jupyter-client==8.6.3
      - jupyter-core==5.7.2
      - jupyter-events==0.12.0
      - jupyter-lsp==2.2.5
      - jupyter-server==2.15.0
      - jupyter-server-terminals==0.5.3
      - jupyterlab==4.3.6
      - jupyterlab-pygments==0.3.0
      - jupyterlab-server==2.27.3
      - locket==1.0.0
      - markdown==3.7
      - markupsafe==3.0.2
      - matplotlib-inline==0.1.7
      - mistune==3.1.3
      - msgpack==1.1.0
      - msgpack-numpy==0.4.8
      - nbclient==0.10.2
      - nbconvert==7.16.6
      - nbformat==5.10.4
      - nest-asyncio==1.6.0
      - networkx==3.2.1
      - notebook==7.3.3
      - notebook-shim==0.2.4
      - numcodecs==0.12.1
      - numpy==2.0.2
      - overrides==7.7.0
      - packaging==24.2
      - pandas==2.2.3
      - pandocfilters==1.5.1
      - panel==0.5.1
      - param==1.13.0
      - parso==0.8.4
      - partd==1.4.2
      - pexpect==4.9.0
      - pillow==11.1.0
      - platformdirs==4.3.7
      - pluggy==1.5.0
      - prometheus-client==0.21.1
      - prompt-toolkit==3.0.50
      - psutil==7.0.0
      - ptyprocess==0.7.0
      - pure-eval==0.2.3
      - pyarrow==19.0.1
      - pycparser==2.22
      - pyct==0.5.0
      - pygments==2.19.1
      - pytest==8.3.5
      - python-dateutil==2.9.0.post0
      - python-json-logger==3.3.0
      - python-snappy==0.7.3
      - pytz==2025.2
      - pyviz-comms==3.0.4
      - pyyaml==6.0.2
      - pyzmq==26.3.0
      - referencing==0.36.2
      - requests==2.32.3
      - rfc3339-validator==0.1.4
      - rfc3986-validator==0.1.1
      - rpds-py==0.24.0
      - send2trash==1.8.3
      - six==1.17.0
      - sniffio==1.3.1
      - soupsieve==2.6
      - stack-data==0.6.3
      - terminado==0.18.1
      - testpath==0.3.1
      - tinycss2==1.4.0
      - tomli==2.2.1
      - toolz==1.0.0
      - tornado==6.4.2
      - traitlets==5.14.3
      - types-python-dateutil==2.9.0.20241206
      - typing-extensions==4.13.0
      - tzdata==2025.2
      - uri-template==1.3.0
      - urllib3==2.3.0
      - wcwidth==0.2.13
      - webcolors==24.11.1
      - webencodings==0.5.1
      - websocket-client==1.8.0
      - xyzservices==2025.1.0
      - zarr==2.18.2
      - zipp==3.21.0
prefix: /opt/conda/envs/intake

intake/container/tests/test_persist.py::test_persist_with_nonnumeric_ttl_raises_error
intake/container/tests/test_persist.py::test_undask_persist
intake/container/tests/test_persist.py::test_store intake/container/tests/test_persist.py::test_backtrack
intake/source/base.py
intake/source/base.py