Add get_qir_str() method to qsharp.compile() result (#887)

This is to support the scenario where the user wants to generate an
input file to be submitted with the `az quantum` cli.

pip/qsharp/_qsharp.py

@@ -86,10 +86,22 @@ def compile(entry_expr):
 
     :param entry_expr: The Q# expression that will be used as the entrypoint
         for the program.
+
+    :returns QirInputData: The compiled program.
+
+    To get the QIR string from the compiled program, use `str()`.
+
+    Example:
+
+    .. code-block:: python
+        program = qsharp.compile("...")
+        with open('myfile.ll', 'w') as file:
+            file.write(str(program))
     """
     ll_str = get_interpreter().qir(entry_expr)
     return QirInputData("main", ll_str)
 
+
 def estimate(entry_expr, params: Union[dict, List, EstimatorParams] = None) -> EstimatorResult:
     """
     Estimates resources for Q# source code.
@@ -112,6 +124,7 @@ def estimate(entry_expr, params: Union[dict, List, EstimatorParams] = None) -> E
         json.loads(get_interpreter().estimate(entry_expr, json.dumps(params)))
     )
 
+
 def dump_machine() -> StateDump:
     """
     Returns the sparse state vector of the simulator as a StateDump object.
@@ -140,3 +153,6 @@ def __init__(self, name: str, ll_str: str):
     # by the protocol and must remain unchanged.
     def _repr_qir_(self, **kwargs) -> bytes:
         return self._ll_str.encode("utf-8")
+
+    def __str__(self) -> str:
+        return self._ll_str

pip/tests/test_qsharp.py

@@ -32,6 +32,7 @@ def test_stdout_multiple_lines() -> None:
 
     assert f.getvalue() == "STATE:\n|0⟩: 1.0000+0.0000𝑖\nHello!\n"
 
+
 def test_dump_machine() -> None:
     qsharp.init(target_profile=qsharp.TargetProfile.Full)
     qsharp.eval(
@@ -58,3 +59,11 @@ def test_compile_qir_input_data() -> None:
     operation = qsharp.compile("Program()")
     qir = operation._repr_qir_()
     assert isinstance(qir, bytes)
+
+
+def test_compile_qir_str() -> None:
+    qsharp.init(target_profile=qsharp.TargetProfile.Base)
+    qsharp.eval("operation Program() : Result { use q = Qubit(); return M(q) }")
+    operation = qsharp.compile("Program()")
+    qir = str(operation)
+    assert "define void @ENTRYPOINT__main()" in qir