为什么要用python链接HDFS

我们的目标是大数据算法平台，我们在处理数据，训练模型后，部分数据需要存在hdfs，那么我们就可以直接通过python 接口把数据放在hdfs上。

教程

Python hdfs包_程序模块 - PyPI - Python中文网

安装

pip install  requests-kerberos
pip install kerberos
pip install avro
pip install hdfs 

安装过程存在问题

cannot import name 'SCHEME_KEYS'

重新安装pip即可

conda remove pip 
conda install pip

使用方法

 hdfscli模式

click模式有什么好处，其实可以看做python的cmd模式，具体可以参考Options — Click Documentation (6.x)

这里可以自行查一下click与args的区别。

Quickstart — HdfsCLI 2.5.8 documentation

新增配置， vim ~/.hdfscli.cfg

[global]
default.alias = dev

[dev.alias]
url = http://localhost:50070
user = root

hdfscli功能

 hdfscli --help

Usage:
  hdfscli [interactive] [-a ALIAS] [-v...]
  hdfscli download [-fsa ALIAS] [-v...] [-t THREADS] HDFS_PATH LOCAL_PATH
  hdfscli upload [-sa ALIAS] [-v...] [-A | -f] [-t THREADS] LOCAL_PATH HDFS_PATH
  hdfscli -L | -V | -h


Commands:
  download                      Download a file or folder from HDFS. If a
                                single file is downloaded, - can be
                                specified as LOCAL_PATH to stream it to
                                standard out.
  interactive                   Start the client and expose it via the python
                                interpreter (using iPython if available).
  upload                        Upload a file or folder to HDFS. - can be
                                specified as LOCAL_PATH to read from standard
                                in.

 进入hdfscli

hdfscli --alias=dev

WebHDFS API

 我们知道在hdfs中，经常用的命令有

hadoop fs -ls
hadoop fs -cat
hadoop fs -put
hadoop fs -get
hadoop fs -mkdir
hadoop fs -cp
hadoop fs -mv
hadoop fs -stat

在python中也要实现上述功能

from hdfs import Client
client=Client("http://localhost:50070/")
dir(client)
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__registry__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', '_allow_snapshot', '_append', '_create', '_create_snapshot', '_delete', '_delete_snapshot', '_disallow_snapshot', '_get_acl_status', '_get_content_summary', '_get_file_checksum', '_get_file_status', '_get_home_directory', '_get_trash_root', '_list_status', '_lock', '_mkdirs', '_modify_acl_entries', '_open', '_proxy', '_remove_acl', '_remove_acl_entries', '_remove_default_acl', '_rename', '_rename_snapshot', '_request', '_session', '_set_acl', '_set_owner', '_set_permission', '_set_replication', '_set_times', '_timeout', '_urls', 'acl_status', 'allow_snapshot', 'checksum', 'content', 'create_snapshot', 'delete', 'delete_snapshot', 'disallow_snapshot', 'download', 'from_options', 'list', 'makedirs', 'parts', 'read', 'remove_acl', 'remove_acl_entries', 'remove_default_acl', 'rename', 'rename_snapshot', 'resolve', 'root', 'set_acl', 'set_owner', 'set_permission', 'set_replication', 'set_times', 'status', 'upload', 'url', 'urls', 'walk', 'write']

具体如何使用，直接看python文档说明即可。

注意，这里的URL最后要加上反斜杠，要不然会报错。

其他参考文档

python读写hdfs四种不同格式文件 - 简书