Import ROOT functions only where needed

* Allows basic hepdata_lib functionality to work without ROOT.
* Need to disable pylint "import-outside-toplevel" error.

hepdata_lib/c_file_reader.py

@@ -2,7 +2,6 @@
 import io
 from array import array
 from future.utils import raise_from
-from ROOT import TGraph, TGraphErrors
 import hepdata_lib.root_utils as ru
 from hepdata_lib.helpers import check_file_existence
 
@@ -137,6 +136,8 @@ def create_tgrapherrors(self, x_value, y_value, dx_value, dy_value):
         """Function to create pyroot TGraphErrors object"""
         # pylint: disable=no-self-use
 
+        from ROOT import TGraphErrors  # pylint: disable=import-outside-toplevel
+
         # Creating pyroot TGraphErrors object
         x_values = array('i')
         y_values = array('i')
@@ -173,6 +174,8 @@ def create_tgraph(self, x_value, y_value):
         """Function to create pyroot TGraph object"""
         # pylint: disable=no-self-use
 
+        from ROOT import TGraph  # pylint: disable=import-outside-toplevel
+
         # Creating pyroot TGraph object
         x_values = array('i')
         y_values = array('i')

hepdata_lib/root_utils.py

@@ -3,7 +3,6 @@
 import ctypes
 from future.utils import raise_from
 import numpy as np
-import ROOT as r
 from hepdata_lib.helpers import check_file_existence
 
 class RootFileReader:
@@ -31,14 +30,16 @@ def tfile(self, tfile):
         Can either be an already open TFile or a path to the file on disk.
         :type tfile: TFile or str
         """
+        from ROOT import TFile  # pylint: disable=import-outside-toplevel
+
         if isinstance(tfile, str):
             if not tfile.endswith(".root"):
                 raise RuntimeError(
                     "RootFileReader: Input file is not a ROOT file (name does not end in .root)!"
                     )
             if check_file_existence(tfile):
-                self._tfile = r.TFile(tfile)
-        elif isinstance(tfile, r.TFile):
+                self._tfile = TFile(tfile)
+        elif isinstance(tfile, TFile):
             self._tfile = tfile
         else:
             raise ValueError(
@@ -216,8 +217,10 @@ def read_tree(self, path_to_tree, branch_name):
         :returns: list -- The values saved in the tree branch.
 
         """
+        from ROOT import TTree  # pylint: disable=import-outside-toplevel
+
         tree = self.tfile.Get(path_to_tree)
-        if not tree or not isinstance(tree, r.TTree):
+        if not tree or not isinstance(tree, TTree):
             raise RuntimeError(f"No TTree found for path '{path_to_tree}'.")
         values = []
         for event in tree:
@@ -293,6 +296,8 @@ def get_hist_2d_points(hist, **kwargs):
         Symmetric errors are returned if the histogram error option
         TH1::GetBinErrorOption() returns TH1::kNormal.
     """
+    from ROOT import TH1  # pylint: disable=import-outside-toplevel
+
     xlim = kwargs.pop('xlim', (None, None))
     ylim = kwargs.pop('ylim', (None, None))
     force_symmetric_errors = kwargs.pop('force_symmetric_errors', False)
@@ -317,7 +322,7 @@ def get_hist_2d_points(hist, **kwargs):
     ixmax = hist.GetXaxis().FindBin(xlim[1]) if xlim[1] is not None else hist.GetNbinsX() + 1
     iymin = hist.GetYaxis().FindBin(ylim[0]) if ylim[0] is not None else 1
     iymax = hist.GetYaxis().FindBin(ylim[1]) if ylim[1] is not None else hist.GetNbinsY() + 1
-    symmetric = (hist.GetBinErrorOption() == r.TH1.kNormal)
+    symmetric = (hist.GetBinErrorOption() == TH1.kNormal)
     if force_symmetric_errors:
         symmetric = True
     for x_bin in range(ixmin, ixmax):
@@ -374,6 +379,8 @@ def get_hist_1d_points(hist, **kwargs):
         Symmetric errors are returned if the histogram error option
         TH1::GetBinErrorOption() returns TH1::kNormal.
     """
+    from ROOT import TH1  # pylint: disable=import-outside-toplevel
+
     xlim = kwargs.pop('xlim', (None, None))
     force_symmetric_errors = kwargs.pop('force_symmetric_errors', False)
     if kwargs:
@@ -388,7 +395,7 @@ def get_hist_1d_points(hist, **kwargs):
     for key in ["x", "y", "x_edges", "x_labels", "dy"]:
         points[key] = []
 
-    symmetric = (hist.GetBinErrorOption() == r.TH1.kNormal)
+    symmetric = (hist.GetBinErrorOption() == TH1.kNormal)
     if force_symmetric_errors:
         symmetric = True
     ixmin = hist.GetXaxis().FindBin(xlim[0]) if xlim[0] is not None else 1
@@ -428,9 +435,10 @@ def get_graph_points(graph):
         For asymmetric errors, a list of tuples of (down,up) values is given.
 
     """
+    from ROOT import TGraph, TGraphErrors, TGraphAsymmErrors  # pylint: disable=import-outside-toplevel
 
     # Check input
-    if not isinstance(graph, (r.TGraph, r.TGraphErrors, r.TGraphAsymmErrors)):
+    if not isinstance(graph, (TGraph, TGraphErrors, TGraphAsymmErrors)):
         raise TypeError(
             "Expected to input to be TGraph or similar, instead got '{0}'".
             format(type(graph)))
@@ -444,10 +452,10 @@ def get_graph_points(graph):
         graph.GetPoint(i, x_val, y_val)
         points["x"].append(float(x_val.value))
         points["y"].append(float(y_val.value))
-        if isinstance(graph, r.TGraphErrors):
+        if isinstance(graph, TGraphErrors):
             points["dx"].append(graph.GetErrorX(i))
             points["dy"].append(graph.GetErrorY(i))
-        elif isinstance(graph, r.TGraphAsymmErrors):
+        elif isinstance(graph, TGraphAsymmErrors):
             points["dx"].append((-graph.GetErrorXlow(i),
                                  graph.GetErrorXhigh(i)))
             points["dy"].append((-graph.GetErrorYlow(i),