Series.to_hdf(path_or_buf, key, mode='a', complevel=None, complib=None, append=False, format=None, index=True, min_itemsize=None, nan_rep=None, dropna=None, data_columns=None, errors='strict', encoding='UTF-8')[source]

Write the contained data to an HDF5 file using HDFStore.

Hierarchical Data Format (HDF) is self-describing, allowing an application to interpret the structure and contents of a file with no outside information. One HDF file can hold a mix of related objects which can be accessed as a group or as individual objects.

In order to add another DataFrame or Series to an existing HDF file please use append mode and a different a key.


One can store a subclass of DataFrame or Series to HDF5, but the type of the subclass is lost upon storing.

For more information see the user guide.

path_or_bufstr or pandas.HDFStore

File path or HDFStore object.


Identifier for the group in the store.

mode{‘a’, ‘w’, ‘r+’}, default ‘a’

Mode to open file:

  • ‘w’: write, a new file is created (an existing file with the same name would be deleted).

  • ‘a’: append, an existing file is opened for reading and writing, and if the file does not exist it is created.

  • ‘r+’: similar to ‘a’, but the file must already exist.

complevel{0-9}, default None

Specifies a compression level for data. A value of 0 or None disables compression.

complib{‘zlib’, ‘lzo’, ‘bzip2’, ‘blosc’}, default ‘zlib’

Specifies the compression library to be used. As of v0.20.2 these additional compressors for Blosc are supported (default if no compressor specified: ‘blosc:blosclz’): {‘blosc:blosclz’, ‘blosc:lz4’, ‘blosc:lz4hc’, ‘blosc:snappy’, ‘blosc:zlib’, ‘blosc:zstd’}. Specifying a compression library which is not available issues a ValueError.

appendbool, default False

For Table formats, append the input data to the existing.

format{‘fixed’, ‘table’, None}, default ‘fixed’

Possible values:

  • ‘fixed’: Fixed format. Fast writing/reading. Not-appendable, nor searchable.

  • ‘table’: Table format. Write as a PyTables Table structure which may perform worse but allow more flexible operations like searching / selecting subsets of the data.

  • If None, pd.get_option(‘io.hdf.default_format’) is checked, followed by fallback to “fixed”.

errorsstr, default ‘strict’

Specifies how encoding and decoding errors are to be handled. See the errors argument for open() for a full list of options.

encodingstr, default “UTF-8”
min_itemsizedict or int, optional

Map column names to minimum string sizes for columns.

nan_repAny, optional

How to represent null values as str. Not allowed with append=True.

data_columnslist of columns or True, optional

List of columns to create as indexed data columns for on-disk queries, or True to use all columns. By default only the axes of the object are indexed. See Query via data columns. Applicable only to format=’table’.

See also


Read from HDF file.


Write a DataFrame to the binary parquet format.


Write to a SQL table.


Write out feather-format for DataFrames.


Write out to a csv file.


>>> df = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6]},
...                   index=['a', 'b', 'c'])  
>>> df.to_hdf('data.h5', key='df', mode='w')  

We can add another object to the same file:

>>> s = pd.Series([1, 2, 3, 4])  
>>> s.to_hdf('data.h5', key='s')  

Reading from HDF file:

>>> pd.read_hdf('data.h5', 'df')  
A  B
a  1  4
b  2  5
c  3  6
>>> pd.read_hdf('data.h5', 's')  
0    1
1    2
2    3
3    4
dtype: int64