I don't care if it's JSON, pickle, YAML, or whatever.
All other implementations I have seen are not forwards compatible, so if I have a config file, add a new key in the code, then load that config file, it'll just crash.
Are there any simple way to do this?
Configuration files in python
There are several ways to do this depending on the file format required.
ConfigParser [.ini format]
I would use the standard configparser approach unless there were compelling reasons to use a different format.
Write a file like so:
from ConfigParser import SafeConfigParser
config = SafeConfigParser()
config.read('config.ini')
config.add_section('main')
config.set('main', 'key1', 'value1')
config.set('main', 'key2', 'value2')
config.set('main', 'key3', 'value3')
with open('config.ini', 'w') as f:
config.write(f)
The file format is very simple with sections marked out in square brackets:
[main]
key1 = value1
key2 = value2
key3 = value3
Values can be extracted from the file like so:
from ConfigParser import SafeConfigParser
config = SafeConfigParser()
config.read('config.ini')
print config.get('main', 'key1') # -> "value1"
print config.get('main', 'key2') # -> "value2"
print config.get('main', 'key3') # -> "value3"
# getfloat() raises an exception if the value is not a float
a_float = config.getfloat('main', 'a_float')
# getint() and getboolean() also do this for their respective types
an_int = config.getint('main', 'an_int')
JSON [.json format]
JSON data can be very complex and has the advantage of being highly portable.
Write data to a file:
import json
config = {'key1': 'value1', 'key2': 'value2'}
with open('config.json', 'w') as f:
json.dump(config, f)
Read data from a file:
import json
with open('config.json', 'r') as f:
config = json.load(f)
#edit the data
config['key3'] = 'value3'
#write it back to the file
with open('config.json', 'w') as f:
json.dump(config, f)
YAML
A basic YAML example is provided in this answer. More details can be found on the pyYAML website.
If you want to use something like an INI file to hold settings, consider using configparser which loads key value pairs from a text file, and can easily write back to the file.
INI file has the format:
[Section]
key = value
key with spaces = somevalue
ConfigParser Basic example
The file can be loaded and used like this:
#!/usr/bin/env python
import ConfigParser
import io
# Load the configuration file
with open("config.yml") as f:
sample_config = f.read()
config = ConfigParser.RawConfigParser(allow_no_value=True)
config.readfp(io.BytesIO(sample_config))
# List all contents
print("List all contents")
for section in config.sections():
print("Section: %s" % section)
for options in config.options(section):
print("x %s:::%s:::%s" % (options,
config.get(section, options),
str(type(options))))
# Print some contents
print("\nPrint some contents")
print(config.get('other', 'use_anonymous')) # Just get the value
print(config.getboolean('other', 'use_anonymous')) # You know the datatype?
which outputs
List all contents
Section: mysql
x host:::localhost:::<type 'str'>
x user:::root:::<type 'str'>
x passwd:::my secret password:::<type 'str'>
x db:::write-math:::<type 'str'>
Section: other
x preprocessing_queue:::["preprocessing.scale_and_center",
"preprocessing.dot_reduction",
"preprocessing.connect_lines"]:::<type 'str'>
x use_anonymous:::yes:::<type 'str'>
Print some contents
yes
True
As you can see, you can use a standard data format that is easy to read and write. Methods like getboolean and getint allow you to get the datatype instead of a simple string.
Writing configuration
import os
configfile_name = "config.yaml"
# Check if there is already a configurtion file
if not os.path.isfile(configfile_name):
# Create the configuration file as it doesn't exist yet
cfgfile = open(configfile_name, 'w')
# Add content to the file
Config = ConfigParser.ConfigParser()
Config.add_section('mysql')
Config.set('mysql', 'host', 'localhost')
Config.set('mysql', 'user', 'root')
Config.set('mysql', 'passwd', 'my secret password')
Config.set('mysql', 'db', 'write-math')
Config.add_section('other')
Config.set('other',
'preprocessing_queue',
['preprocessing.scale_and_center',
'preprocessing.dot_reduction',
'preprocessing.connect_lines'])
Config.set('other', 'use_anonymous', True)
Config.write(cfgfile)
cfgfile.close()
results in
[mysql]
host = localhost
user = root
passwd = my secret password
db = write-math
[other]
preprocessing_queue = ['preprocessing.scale_and_center', 'preprocessing.dot_reduction', 'preprocessing.connect_lines']
use_anonymous = True
XML Basic example
Seems not to be used at all for configuration files by the Python community. However, parsing / writing XML is easy and there are plenty of possibilities to do so with Python. One is BeautifulSoup:
from BeautifulSoup import BeautifulSoup
with open("config.xml") as f:
content = f.read()
y = BeautifulSoup(content)
print(y.mysql.host.contents[0])
for tag in y.other.preprocessing_queue:
print(tag)
where the config.xml might look like this
<config>
<mysql>
<host>localhost</host>
<user>root</user>
<passwd>my secret password</passwd>
<db>write-math</db>
</mysql>
<other>
<preprocessing_queue>
<li>preprocessing.scale_and_center</li>
<li>preprocessing.dot_reduction</li>
<li>preprocessing.connect_lines</li>
</preprocessing_queue>
<use_anonymous value="true" />
</other>
</config>
Save and load a dictionary. You will have arbitrary keys, values and arbitrary number of key, values pairs.
Try using ReadSettings:
from readsettings import ReadSettings
data = ReadSettings("settings.json") # Load or create any json, yml, yaml or toml file
data["name"] = "value" # Set "name" to "value"
data["name"] # Returns: "value"
来源：https://stackoverflow.com/questions/19078170/python-how-would-you-save-a-simple-settings-config-file