Support single argument version of sqlContext.getConf

## What changes were proposed in this pull request?

In Python, sqlContext.getConf didn't allow getting the system default (getConf with one parameter).

Now the following are supported:
```
sqlContext.getConf(confName)  # System default if not locally set, this is new
sqlContext.getConf(confName, myDefault)  # myDefault if not locally set, old behavior
```

I also added doctests to this function. The original behavior does not change.

## How was this patch tested?

Manually, but doctests were added.

Author: mathieu longtin <mathieu.longtin@nuance.com>

Closes #12488 from mathieulongtin/pyfixgetconf3.

1 files changed, 17 insertions, 3 deletions

diff --git a/python/pyspark/sql/context.py b/python/pyspark/sql/context.py
index 11dfcfe13e..ac98639f3a 100644
--- a/python/pyspark/sql/context.py
+++ b/python/pyspark/sql/context.py
@@ -146,13 +146,27 @@ class SQLContext(object):
         """
         self._ssql_ctx.setConf(key, value)
 
+    @ignore_unicode_prefix
     @since(1.3)
-    def getConf(self, key, defaultValue):
+    def getConf(self, key, defaultValue=None):
         """Returns the value of Spark SQL configuration property for the given key.
 
-        If the key is not set, returns defaultValue.
+        If the key is not set and defaultValue is not None, return
+        defaultValue. If the key is not set and defaultValue is None, return
+        the system default value.
+
+        >>> sqlContext.getConf("spark.sql.shuffle.partitions")
+        u'200'
+        >>> sqlContext.getConf("spark.sql.shuffle.partitions", "10")
+        u'10'
+        >>> sqlContext.setConf("spark.sql.shuffle.partitions", "50")
+        >>> sqlContext.getConf("spark.sql.shuffle.partitions", "10")
+        u'50'
         """
-        return self._ssql_ctx.getConf(key, defaultValue)
+        if defaultValue is not None:
+            return self._ssql_ctx.getConf(key, defaultValue)
+        else:
+            return self._ssql_ctx.getConf(key)
 
     @property
     @since("1.3.1")