Correctly format floats passed to pgf backend.

anntzer · anntzer · commit 00c8a1d2cd38 · 2019-09-08T00:10:37.000+02:00
Using scientific notation (implicitly via "{}".format) results in e.g.
`use("pgf"); figtext(1e-6, 1e-6, "foo"); savefig("/tmp/test.pdf")` lead
to tex failing with
`! Package PGF Math Error: Unknown operator `i' or `in' (in '6.4e-06in').`
diff --git a/lib/matplotlib/backends/backend_pgf.py b/lib/matplotlib/backends/backend_pgf.py
@@ -25,7 +25,9 @@
 _log = logging.getLogger(__name__)
 
 
-###############################################################################
+# Note: When formatting floating point values, it is important to use the
+# %f/{:f} format rather than %s/{} to avoid triggering scientific notation,
+# which is not recognized by TeX.
 
 
 def get_fontspec():
@@ -724,14 +726,14 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
             valign = {"top": "top", "bottom": "bottom",
                       "baseline": "base", "center": ""}
             text_args.extend([
-                f"x={x/dpi}in",
-                f"y={y/dpi}in",
+                f"x={x/dpi:f}in",
+                f"y={y/dpi:f}in",
                 halign[mtext.get_horizontalalignment()],
                 valign[mtext.get_verticalalignment()],
             ])
         else:
             # if not, use the text layout provided by Matplotlib.
-            text_args.append(f"x={x/dpi}in, y={y/dpi}in, left, base")
+            text_args.append(f"x={x/dpi:f}in, y={y/dpi:f}in, left, base")
 
         if angle != 0:
             text_args.append("rotate=%f" % angle)
