def METHOD_NAME(tf_version: str = "") -> dict:
    """Get TensorFlow requirement (CPU) when TF is not installed.
    If tf_version is not given and the environment variable `TENSORFLOW_VERSION` is set, use it as the requirement.
    Parameters
    ----------
    tf_version : str, optional
        TF version
    Returns
    -------
    dict
        TensorFlow requirement, including cpu and gpu.
    """
    if tf_version == "":
        tf_version = os.environ.get("TENSORFLOW_VERSION", "")
    if tf_version == "":
        return {
            "cpu": [
                "tensorflow-cpu; platform_machine!='aarch64' and (platform_machine!='arm64' or platform_system != 'Darwin')",
                "tensorflow; platform_machine=='aarch64' or (platform_machine=='arm64' and platform_system == 'Darwin')",
            ],
            "gpu": [
                "tensorflow",
                "tensorflow-metal; platform_machine=='arm64' and platform_system == 'Darwin'",
            ],
        }
    elif tf_version in SpecifierSet("<1.15") or tf_version in SpecifierSet(
        ">=2.0,<2.1"
    ):
        return {
            "cpu": [
                f"tensorflow=={tf_version}",
            ],
            "gpu": [
                f"tensorflow-gpu=={tf_version}; platform_machine!='aarch64'",
                f"tensorflow=={tf_version}; platform_machine=='aarch64'",
            ],
        }
    else:
        return {
            "cpu": [
                f"tensorflow-cpu=={tf_version}; platform_machine!='aarch64' and (platform_machine!='arm64' or platform_system != 'Darwin')",
                f"tensorflow=={tf_version}; platform_machine=='aarch64'  or (platform_machine=='arm64' and platform_system == 'Darwin')",
            ],
            "gpu": [
                f"tensorflow=={tf_version}",
                "tensorflow-metal; platform_machine=='arm64' and platform_system == 'Darwin'",
            ],
        }