Create datetime.time() object in yaml?

Question

I know that I can create a datetime.datetime object and then use .time() method, like this:

my_file.yaml

MyDateTime: 2015-08-11 10:08:37

and then:

In [58]: f = open("my_file.yaml", "rU")

In [59]: temp = yaml.safe_load(f)

In [60]: f.close()

In [61]: temp['MyDateTime'].time()
Out[61]: datetime.time(10, 8, 37)

but that seems a little redundant, is there a way to create datetime.time() object to begin with?

Answer 1

You can patch the SafeLoader to do your bidding, but it is nicer to make a new Loader that does the same as the SafeLoader used by safe_load(). The only thing you need to provide for that is a method that is invoked (construct_yaml_time()) when a timestamp scalar is matched and specify it by calling add_constructor.

import ruamel.yaml as yaml

from ruamel.yaml.loader import Reader, Scanner, Composer, SafeConstructor, \
     Resolver, Parser

class TimeConstructor(SafeConstructor):
    def __init__(self):
        SafeConstructor.__init__(self)

    def construct_yaml_time(self, node):
        x = SafeConstructor.construct_yaml_timestamp(self, node)
        return x.time()


TimeConstructor.add_constructor(
    u'tag:yaml.org,2002:timestamp',
    TimeConstructor.construct_yaml_time)

class TimeLoader(Reader, Scanner, Parser, Composer, TimeConstructor, Resolver):
    def __init__(self, stream):
        Reader.__init__(self, stream)
        Scanner.__init__(self)
        Parser.__init__(self)
        Composer.__init__(self)
        TimeConstructor.__init__(self)
        Resolver.__init__(self)

yaml_str = """\
MyDateTime: 2015-08-11 10:08:37
x: 23423
"""

data = yaml.load(yaml_str, Loader=TimeLoader)
print data

gives you:

<type 'datetime.time'>
{'x': 23423, 'MyDateTime': datetime.time(10, 8, 37)}

---

You can also specify your time objects as 10:08:37 but this will load them as sexagesimal number and that will convert them to an integer (36517 in this case). You can, of course, change this behaviour as well:

import ruamel.yaml as yaml

from ruamel.yaml.loader import Reader, Scanner, Composer, SafeConstructor, \
     Resolver, Parser

import datetime

class TimeConstructor(SafeConstructor):
    def __init__(self):
        SafeConstructor.__init__(self)

    def construct_yaml_time(self, node):
        value = self.construct_scalar(node)
        if ':' not in value:
            return SafeConstructor.construct_yaml_int(self, node)
        return datetime.time(*[int(x) for x in value.split(':')])



TimeConstructor.add_constructor(
    u'tag:yaml.org,2002:int',
    TimeConstructor.construct_yaml_time)

class TimeLoader(Reader, Scanner, Parser, Composer, TimeConstructor, Resolver):
    def __init__(self, stream):
        Reader.__init__(self, stream)
        Scanner.__init__(self)
        Parser.__init__(self)
        Composer.__init__(self)
        TimeConstructor.__init__(self)
        Resolver.__init__(self)

yaml_str = """\
MyDateTime: 10:08:37
x: 12345
"""

data = yaml.load(yaml_str, Loader=TimeLoader)
print data

which gives:

{'x': 12345, 'MyDateTime': datetime.time(10, 8, 37)}

This relies on the time to be recognised by the normal int recogniser. You can also recognise the sexagesimal itself, but that is more complex to implement in my experience.

---

Other alternatives exists, including creating datetime.time objects by tagging them explicitly and providing loading (and possible saving) routines.