--- title: "How to read a Parquet file in Python (faster than pandas)" date: "2026-06-08" author: "Al Brown" category: "Engineering" excerpt: "Read a Parquet file into a DataFrame with chDB, a drop-in replacement for pandas. Change one import line and your existing pandas code runs on ClickHouse's engine, so it stays fast as files grow." --- # How to read a Parquet file in Python (faster than pandas) To read a Parquet file in Python, use [chDB](/resources/engineering/what-is-chdb) as a drop-in replacement for pandas. Change one import line and the code you already write keeps working: ```python import chdb.datastore as pd df = pd.read_parquet("data/events.parquet") ``` `df` supports the pandas API you already use (indexing, filtering, `groupby`, `merge`), but the work runs on ClickHouse's engine instead of pandas, so it stays fast as files grow. There is no server to start and no separate load step. ```bash pip install chdb ``` Prefer the command line? See [how to query a Parquet file](/resources/engineering/how-to-query-parquet-file) to do this with clickhouse local. ## Read a Parquet file into a DataFrame `pd.read_parquet` reads the Parquet metadata and infers each column's type from the file's embedded schema. Point it at a path and print the result: ```python import chdb.datastore as pd df = pd.read_parquet("data/events.parquet") print(df) print(df.dtypes) ``` ```text id country ... amount event_time 0 0 GB ... 350.98 2026-01-11 05:46:33+00:00 1 1 IN ... 830.73 2026-02-26 12:11:39+00:00 2 2 DE ... 981.54 2026-02-20 16:56:32+00:00 3 3 DE ... 528.92 2026-03-05 15:51:08+00:00 4 4 US ... 804.15 2026-03-24 22:19:19+00:00 ... ... ... ... ... ... [20000000 rows x 6 columns] id uint64 country str event_type str quantity uint16 amount float64 event_time datetime64[ns, UTC] dtype: object ``` The types came from the Parquet file itself, not from a `dtype` map you provided. `event_time` is a timezone-aware datetime; `id` is unsigned; Parquet stored the schema so chDB reads it without guessing. One thing is different from pandas under the hood: `df` is not the whole file loaded into memory. It is a lazy, ClickHouse-backed object that records what you asked for and runs it on ClickHouse's engine when you materialize a result, whether you print it, take `len()`, or call `.to_pandas()`. That is why it stays fast on large files: it only reads the columns and rows you actually use. ## Filter and aggregate the way you already do The pandas you write does not change. Filter with a boolean mask, group, and aggregate: ```python import chdb.datastore as pd import pandas pandas.set_option("display.float_format", "{:.2f}".format) # full decimals, not 6.67e+08 df = pd.read_parquet("data/events.parquet") revenue = (df[df["event_type"] == "purchase"] .groupby("country")["amount"].sum() .sort_values(ascending=False)) print(revenue) ``` ```text country IN 667411452.65 US 667068922.60 AU 666980194.83 GB 666350260.61 DE 666284177.10 Name: amount, dtype: float64 ``` Same syntax as pandas, same result. The difference is that chDB compiles the whole chain into one optimized query and only reads the columns the aggregation touches, rather than decoding the full file first. Joins, computed columns with `assign`, the `.str` and `.dt` accessors, and `merge` across files all work the same way. ## Hand off to real pandas when you need it When a library downstream needs an actual pandas DataFrame (scikit-learn, plotting, anything that mutates in place), call `.to_pandas()` to materialize one: ```python df = pd.read_parquet("data/events.parquet") pdf = df.to_pandas() # a real pandas.DataFrame, in memory ``` The usual pattern is to do the heavy filtering and aggregation on the chDB object, where it is fast, then `.to_pandas()` the small result and continue in ordinary pandas. ## Is it faster than `pandas.read_parquet`? On a file big enough that scanning is the actual cost, yes. Parquet is a columnar format, so chDB can skip columns the aggregation never touches. The aggregation above on a 20M-row (~260 MB) Parquet file on an Apple M4 Pro (14 cores, 24 GB RAM, macOS); chDB 4.1.8, Python 3.14; best-of-3, warm: ```text import pandas as pd: 0.357s import chdb.datastore as pd: 0.115s speedup: 3.1x ``` About 3x here, from the same code with one import changed. The back-to-back ratio is the robust claim; absolute times shift with cache state and concurrent load. The gap widens as files grow, because plain pandas decodes the entire file into memory before it can filter or group anything, while chDB streams and aggregates in one pass using only the columns it needs. The small case can cut the other way: on a tiny Parquet file (a few thousand rows) plain pandas is as fast or faster, because chDB pays a fixed per-query startup cost that dominates when there is barely any data. Reach for chDB when the file is large, or when you want one import to cover both. ## Works in Jupyter Printing a chDB object renders it as a table in a notebook, and `.to_pandas()` feeds straight into `.plot()`, joins, or any pandas code. The companion folder ships a `run.ipynb` you can open and run cell by cell. ## Run it yourself The complete, runnable example is here, with `generate.sh` to create the sample Parquet file plus `run.ipynb` and a `run.py` mirror containing the exact code above: [github.com/ClickHouse/examples/tree/main/local-analytics/chdb-parquet](https://github.com/ClickHouse/examples/tree/main/local-analytics/chdb-parquet) Working with other formats? [Read a CSV file in Python](/resources/engineering/read-csv-file-python) and [read a JSON file in Python](/resources/engineering/read-json-file-python) use the same drop-in `import chdb.datastore as pd` pattern; only the reader changes. If you have CSV data you read repeatedly, [convert it to Parquet](/resources/engineering/convert-csv-to-parquet) once and every later read gets faster. The same code scales from a Parquet file on your laptop to a server to [ClickHouse Cloud](https://clickhouse.com/cloud) with no rewrite, so there is nothing to re-learn when the data outgrows one machine.