Can python fastparquet module read in compressed parquet file?

Question

Our parquet files are stored in aws S3 bucket and are compressed by SNAPPY. I was able to use python fastparquet module to read in the uncompressed version of the parquet file but not the compressed version.

This is the code I am using for uncompressed

s3 = s3fs.S3FileSystem(key='XESF',    secret='dsfkljsf')
myopen = s3.open
pf = ParquetFile('sample/py_test_snappy/part-r-12423423942834.parquet', open_with=myopen)
df=pf.to_pandas()

This return no error but when I am trying to read in the snappy compressed version of the file:

pf = ParquetFile('sample/py_test_snappy/part-r-12423423942834.snappy.parquet', open_with=myopen)

I got error with to_pandas()

df=pf.to_pandas()

Error message

KeyErrorTraceback (most recent call last) in () ----> 1 df=pf.to_pandas()

/opt/conda/lib/python3.5/site-packages/fastparquet/api.py in to_pandas(self, columns, categories, filters, index) 293 for (name, v) in views.items()} 294 self.read_row_group(rg, columns, categories, infile=f, --> 295 index=index, assign=parts) 296 start += rg.num_rows 297 else:

/opt/conda/lib/python3.5/site-packages/fastparquet/api.py in read_row_group(self, rg, columns, categories, infile, index, assign) 151 core.read_row_group( 152 infile, rg, columns, categories, self.helper, self.cats, --> 153 self.selfmade, index=index, assign=assign) 154 if ret: 155 return df

/opt/conda/lib/python3.5/site-packages/fastparquet/core.py in read_row_group(file, rg, columns, categories, schema_helper, cats, selfmade, index, assign) 300 raise RuntimeError('Going with pre-allocation!') 301 read_row_group_arrays(file, rg, columns, categories, schema_helper, --> 302 cats, selfmade, assign=assign) 303 304 for cat in cats:

/opt/conda/lib/python3.5/site-packages/fastparquet/core.py in read_row_group_arrays(file, rg, columns, categories, schema_helper, cats, selfmade, assign) 289 read_col(column, schema_helper, file, use_cat=use, 290 selfmade=selfmade, assign=out[name], --> 291 catdef=out[name+'-catdef'] if use else None) 292 293

/opt/conda/lib/python3.5/site-packages/fastparquet/core.py in read_col(column, schema_helper, infile, use_cat, grab_dict, selfmade, assign, catdef) 196 dic = None 197 if ph.type == parquet_thrift.PageType.DICTIONARY_PAGE: --> 198 dic = np.array(read_dictionary_page(infile, schema_helper, ph, cmd)) 199 ph = read_thrift(infile, parquet_thrift.PageHeader) 200 dic = convert(dic, se)

/opt/conda/lib/python3.5/site-packages/fastparquet/core.py in read_dictionary_page(file_obj, schema_helper, page_header, column_metadata) 152 Consumes data using the plain encoding and returns an array of values. 153 """ --> 154 raw_bytes = _read_page(file_obj, page_header, column_metadata) 155 if column_metadata.type == parquet_thrift.Type.BYTE_ARRAY: 156 # no faster way to read variable-length-strings?

/opt/conda/lib/python3.5/site-packages/fastparquet/core.py in _read_page(file_obj, page_header, column_metadata) 28 """Read the data page from the given file-object and convert it to raw, uncompressed bytes (if necessary).""" 29 raw_bytes = file_obj.read(page_header.compressed_page_size) ---> 30 raw_bytes = decompress_data(raw_bytes, column_metadata.codec) 31 32 assert len(raw_bytes) == page_header.uncompressed_page_size, \

/opt/conda/lib/python3.5/site-packages/fastparquet/compression.py in decompress_data(data, algorithm) 48 def decompress_data(data, algorithm='gzip'): 49 if isinstance(algorithm, int): ---> 50 algorithm = rev_map[algorithm] 51 if algorithm.upper() not in decompressions: 52 raise RuntimeError("Decompression '%s' not available. Options: %s" %

KeyError: 1

Answer 1

The error likely indicates that the library for decompressing SNAPPY was not found on your system - although clearly the error message could be clearer!

Depending on your system, the following lines may solve this for you:

conda install python-snappy

or

pip install python-snappy

If you are on windows, the build chain may not work, and perhaps you need to install from here.