How to import python class

[tqq1994516]

I try to get the class in python lib, the code is as follows

from python import Python

fn main():
    try:
        let pydantic = Python.import_module("pydantic")
        print(pydantic.BaseModel)
    except e:
        print("failed to show plot:", e.value)

but get this error

failed to show plot: An error occurred in Python.

[rarebreed]

Did you pip install pydantic? I generally always create a virtualenv first, activate it, and run my mojo. If you're in VS code, make sure you select the virtualenv also

[tqq1994516]

I can print pydantic variable object，but if me print pydantic.BaseModel, I will get this error.

[tqq1994516]

I can print pydantic variable object，but if me print pydantic.BaseModel, I will get this error.

[rarebreed]

I can print pydantic variable object，but if me print pydantic.BaseModel, I will get this error.

In the except clause, I just did print(e.value) and I got this error (using python 3.11.5)

❯ mojo run main.mojo
No string method found on the python object.

so, mojo's print is not the same as python's print. In python, the print() function will implicitly do something like this

# this is python
import pydantic as pd
print(str(pd.BaseModel))

From the python docs

All non-keyword arguments are converted to strings like str() does and written to the stream

In mojo, the print function works with mojo types, though it does have an overloaded type for object. My guess is that the mojo print doesn't do the implicit call to str. Not sure if that is a bug, or a "not implemented yet" feature.

But you can try this workaround

fn main():
    try:
        let pydantic = Python.import_module("pydantic")
        let bi = Python.import_module("builtins")
        print(bi.str(pydantic.BaseModel))
        # or bi.print(pd.BaseModel)
    except e:
        print("failed to show plot:", e.value)

[tqq1994516]

What you said is indeed correct, and the pydantic.BaseModel cannot be instantiated directly, which makes me think that the class cannot be imported. I changed the class instantiation and use of another library and there is no problem.