Metview's Python interface provides access to all of Metview's Macro language functions, with automatic translations between data types. Here's an example that shows how to retrieve model and observation data and compute their difference, and the weighted mean value of that difference, both in Macro and in Python.

# Metview Macro

t2m_fc48 = retrieve(
    type    : "fc",
    levtype : "sfc",
    param   : "2t",
    date    : -5,
    step    : 48,
    grid    : "o1280")

synop = retrieve(
    type   : "ob",
    repres : "bu",
    date   : -3)

synop_t2m = obsfilter(
    output    : "geopoints",
    parameter : 012004,
    data      : synop)

diff = t2m_fc48 - synop_t2m
print(integrate(diff))

import metview as mv

t2m_fc48 = mv.retrieve(
    type    = "fc",
    levtype = "sfc",
    param   = "2t",
    date    = -5,
    step    = 48,
    grid    = "o1280")

synop = mv.retrieve(
    type   = "ob",
    repres = "bu",
    date   = -3)

synop_t2m = mv.obsfilter(
    output    = "geopoints",
    parameter = "012004",
    data      = synop)

diff = t2m_fc48 - synop_t2m
print(mv.integrate(diff))

You can see that the Macro functions are all available through the namespace defined in the import command.

More examples are available in the Python the Gallery (Redundant).

Variable types

When calling Macro functions from Python, variables passed as input to or output from those functions undergo a conversion as described in this table:

Additional data export features

...

Macro functions which correspond to icons, such as retrieve(), which corresponds to the Mars Retrieval icon, can take their arguments in a number of ways:

Object-oriented calling

Metview's Python interface also provides a more object-oriented way of using the wrapper classes such as Fieldset. The following two snippets of code are equivalent:

Calling user-defined Macro functions from Python

...

• Macro indexing starts at 1, but Python indexing starts at 0. Aside from the standard Python structures such as lists, this is also true for Metview Python classes such as Fieldset. Given a fieldset fs, the first field is obtained in Macro by fs[1], but in Python it is obtained by fs[0].
• In order to support the more interactive coding environments provided by Python, any call to the plot() command will immediately produce a plot. This is different from Macro, where plots are delayed until the end. The result of this is that multiple plot() commands in Python will result in multiple plot windows. Fortunately, a single plot() command can be given any number of items, including multiple pages. To see how to produce a multi-plot layout, please see the Layoutx3 In Python gallery Example gallery example.