From 01355d59fc22860de0d7f04b86318944643ba0f6 Mon Sep 17 00:00:00 2001
From: Alexander Haupt <1485187+elrubio@users.noreply.github.com>
Date: Fri, 9 Feb 2018 18:39:20 +0100
Subject: [PATCH] BUG: Fix 'left' join turned into 'outer' join when joining
 with a sequence of dataframes (#19607)

---
 pandas/core/frame.py | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index 6d8dcb8a1ca89..a6417f821a4e6 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -5328,18 +5328,17 @@ def _join_compat(self, other, on=None, how='left', lsuffix='', rsuffix='',
                 raise ValueError('Joining multiple DataFrames only supported'
                                  ' for joining on index')
 
-            # join indexes only using concat
-            if how == 'left':
-                how = 'outer'
-                join_axes = [self.index]
-            else:
-                join_axes = None
-
             frames = [self] + list(other)
 
             can_concat = all(df.index.is_unique for df in frames)
 
+            # join indexes only using concat
             if can_concat:
+                if how == 'left':
+                    how = 'outer'
+                    join_axes = [self.index]
+                else:
+                    join_axes = None
                 return concat(frames, axis=1, join=how, join_axes=join_axes,
                               verify_integrity=True)