Source code for dask.bytes.core

from __future__ import annotations

import copy
import os

from fsspec.core import OpenFile, get_fs_token_paths
from fsspec.utils import infer_compression, read_block

from dask.base import tokenize
from dask.delayed import delayed
from dask.utils import is_integer, parse_bytes

[docs]def read_bytes( urlpath, delimiter=None, not_zero=False, blocksize="128 MiB", sample="10 kiB", compression=None, include_path=False, **kwargs, ): """Given a path or paths, return delayed objects that read from those paths. The path may be a filename like ``'2015-01-01.csv'`` or a globstring like ``'2015-*-*.csv'``. The path may be preceded by a protocol, like ``s3://`` or ``hdfs://`` if those libraries are installed. This cleanly breaks data by a delimiter if given, so that block boundaries start directly after a delimiter and end on the delimiter. Parameters ---------- urlpath : string or list Absolute or relative filepath(s). Prefix with a protocol like ``s3://`` to read from alternative filesystems. To read from multiple files you can pass a globstring or a list of paths, with the caveat that they must all have the same protocol. delimiter : bytes An optional delimiter, like ``b'\\n'`` on which to split blocks of bytes. not_zero : bool Force seek of start-of-file delimiter, discarding header. blocksize : int, str Chunk size in bytes, defaults to "128 MiB" compression : string or None String like 'gzip' or 'xz'. Must support efficient random access. sample : int, string, or boolean Whether or not to return a header sample. Values can be ``False`` for "no sample requested" Or an integer or string value like ``2**20`` or ``"1 MiB"`` include_path : bool Whether or not to include the path with the bytes representing a particular file. Default is False. **kwargs : dict Extra options that make sense to a particular storage connection, e.g. host, port, username, password, etc. Examples -------- >>> sample, blocks = read_bytes('2015-*-*.csv', delimiter=b'\\n') # doctest: +SKIP >>> sample, blocks = read_bytes('s3://bucket/2015-*-*.csv', delimiter=b'\\n') # doctest: +SKIP >>> sample, paths, blocks = read_bytes('2015-*-*.csv', include_path=True) # doctest: +SKIP Returns ------- sample : bytes The sample header blocks : list of lists of ``dask.Delayed`` Each list corresponds to a file, and each delayed object computes to a block of bytes from that file. paths : list of strings, only included if include_path is True List of same length as blocks, where each item is the path to the file represented in the corresponding block. """ if not isinstance(urlpath, (str, list, tuple, os.PathLike)): raise TypeError("Path should be a string, os.PathLike, list or tuple") fs, fs_token, paths = get_fs_token_paths(urlpath, mode="rb", storage_options=kwargs) if len(paths) == 0: raise OSError("%s resolved to no files" % urlpath) if blocksize is not None: if isinstance(blocksize, str): blocksize = parse_bytes(blocksize) if not is_integer(blocksize): raise TypeError("blocksize must be an integer") blocksize = int(blocksize) if blocksize is None: offsets = [[0]] * len(paths) lengths = [[None]] * len(paths) else: offsets = [] lengths = [] for path in paths: if compression == "infer": comp = infer_compression(path) else: comp = compression if comp is not None: raise ValueError( "Cannot do chunked reads on compressed files. " "To read, set blocksize=None" ) size =["size"] if size is None: raise ValueError( "Backing filesystem couldn't determine file size, cannot " "do chunked reads. To read, set blocksize=None." ) elif size == 0: # skip empty offsets.append([]) lengths.append([]) else: # shrink blocksize to give same number of parts if size % blocksize and size > blocksize: blocksize1 = size / (size // blocksize) else: blocksize1 = blocksize place = 0 off = [0] length = [] # figure out offsets, spreading around spare bytes while size - place > (blocksize1 * 2) - 1: place += blocksize1 off.append(int(place)) length.append(off[-1] - off[-2]) length.append(size - off[-1]) if not_zero: off[0] = 1 length[0] -= 1 offsets.append(off) lengths.append(length) delayed_read = delayed(read_block_from_file) out = [] for path, offset, length in zip(paths, offsets, lengths): token = tokenize(fs_token, delimiter, path, fs.ukey(path), compression, offset) keys = [f"read-block-{o}-{token}" for o in offset] values = [ delayed_read( OpenFile(fs, path, compression=compression), o, l, delimiter, dask_key_name=key, ) for o, key, l in zip(offset, keys, length) ] out.append(values) if sample: if sample is True: sample = "10 kiB" # backwards compatibility if isinstance(sample, str): sample = parse_bytes(sample) with OpenFile(fs, paths[0], compression=compression) as f: # read block without seek (because we start at zero) if delimiter is None: sample = else: sample_buff = while True: new = if not new: break if delimiter in new: sample_buff = ( sample_buff + new.split(delimiter, 1)[0] + delimiter ) break sample_buff = sample_buff + new sample = sample_buff if include_path: return sample, out, paths return sample, out
def read_block_from_file(lazy_file, off, bs, delimiter): with copy.copy(lazy_file) as f: if off == 0 and bs is None: return return read_block(f, off, bs, delimiter)