Describe the bug
I'm trying to use datamodel-codegen to generate Pydantic models from Stripe's openapi. The generation itself succeeds but trying to import the generated package results in an import error due to circular dependency:

In [1]: import stripe_api
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
Input In [1], in <cell line: 1>()
----> 1 import stripe_api

File .../stripe_api/__init__.py:13, in <module>
      9 from typing import Any, Dict, List, Optional, Union
     11 from pydantic import BaseModel, Field, constr
---> 13 from . import issuing, test_helpers, treasury
     16 class BusinessType(Enum):
     17     company = 'company'

File .../stripe_api/issuing.py:12, in <module>
      8 from typing import Dict, List, Optional, Union
     10 from pydantic import BaseModel, Field, constr
---> 12 from . import (
     13     BalanceTransaction,
     14     IssuingAuthorizationAmountDetails,
     15     IssuingAuthorizationMerchantData,
     16     IssuingAuthorizationPendingRequest,
     17     IssuingAuthorizationRequest,
     18     IssuingAuthorizationTreasury,
     19     IssuingAuthorizationVerificationData,
     20     IssuingCardAuthorizationControls,
     21     IssuingCardholderAddress,
     22     IssuingCardholderAuthorizationControls,
     23     IssuingCardholderCompany,
     24     IssuingCardholderIndividual,
     25     IssuingCardholderRequirements,
     26     IssuingCardShipping,
     27     IssuingCardWallets,
     28     IssuingDisputeEvidence,
     29     IssuingDisputeTreasury,
     30     IssuingTransactionAmountDetails,
     31     IssuingTransactionPurchaseDetails,
     32     IssuingTransactionTreasury,
     33 )
     36 class AuthorizationMethod(Enum):
     37     chip = 'chip'

ImportError: cannot import name 'BalanceTransaction' from partially initialized module 'stripe_api' (most likely due to a circular import) (.../stripe_api/__init__.py)

It looks like the generation puts every model that includes a . for example issuing.authorization in its own file, in this example issuing.py, and every model that doesn't - in the __init__.py file, resulting in some models from the init trying to import files from other files, and those other files trying to import from the init.

Trying to generate everything into one file fails with Modular references require an output directory, not a file.

To Reproduce

Example schema:
I tried using both the .yaml and .json just in case, both result in the same error.

Used commandline:

$ datamodel-codegen --input stripe-openapi/openapi/spec3.yaml --output stripe_api

Expected behavior
I'd expect to be able to import the generated code

Version:

• OS: macOS Monterey 12.5
• Python version: 3.9.13
• datamodel-code-generator version: 0.13.1