Merge pull request #8340 from jorisvandenbossche/sql-pep8

CLN: pep8 clean up of sql.py

Author: jorisvandenbossche

pandas/io/sql.py

@@ -1,26 +1,28 @@
+# -*- coding: utf-8 -*-
 """
 Collection of query wrappers / abstractions to both facilitate data
 retrieval and to reduce dependency on DB-specific API.
 """
+
 from __future__ import print_function, division
-from datetime import datetime, date, timedelta
+from datetime import datetime, date
 
 import warnings
 import traceback
-import itertools
 import re
 import numpy as np
 
 import pandas.lib as lib
 import pandas.core.common as com
 from pandas.compat import lzip, map, zip, raise_with_traceback, string_types
 from pandas.core.api import DataFrame, Series
-from pandas.core.common import notnull, isnull
+from pandas.core.common import isnull
 from pandas.core.base import PandasObject
 from pandas.tseries.tools import to_datetime
 
 from contextlib import contextmanager
 
+
 class SQLAlchemyRequired(ImportError):
     pass
 
@@ -34,6 +36,7 @@ class DatabaseError(IOError):
 
 _SQLALCHEMY_INSTALLED = None
 
+
 def _is_sqlalchemy_engine(con):
     global _SQLALCHEMY_INSTALLED
     if _SQLALCHEMY_INSTALLED is None:
@@ -80,7 +83,8 @@ def _handle_date_column(col, format=None):
     else:
         if format in ['D', 's', 'ms', 'us', 'ns']:
             return to_datetime(col, coerce=True, unit=format)
-        elif issubclass(col.dtype.type, np.floating) or issubclass(col.dtype.type, np.integer):
+        elif (issubclass(col.dtype.type, np.floating)
+                or issubclass(col.dtype.type, np.integer)):
             # parse dates as timestamp
             format = 's' if format is None else format
             return to_datetime(col, coerce=True, unit=format)
@@ -89,8 +93,9 @@ def _handle_date_column(col, format=None):
 
 
 def _parse_date_columns(data_frame, parse_dates):
-    """ Force non-datetime columns to be read as such.
-        Supports both string formatted and integer timestamp columns
+    """
+    Force non-datetime columns to be read as such.
+    Supports both string formatted and integer timestamp columns
     """
     # handle non-list entries for parse_dates gracefully
     if parse_dates is True or parse_dates is None or parse_dates is False:
@@ -152,6 +157,7 @@ def _safe_fetch(cur):
         if excName == 'OperationalError':
             return []
 
+
 def tquery(sql, con=None, cur=None, retry=True):
     """
     DEPRECATED. Returns list of tuples corresponding to each row in given sql
@@ -209,8 +215,8 @@ def tquery(sql, con=None, cur=None, retry=True):
 
 def uquery(sql, con=None, cur=None, retry=True, params=None):
     """
-    DEPRECATED. Does the same thing as tquery, but instead of returning results, it
-    returns the number of rows affected.  Good for update queries.
+    DEPRECATED. Does the same thing as tquery, but instead of returning
+    results, it returns the number of rows affected.  Good for update queries.
 
     To obtain the same result in the future, you can use the following:
 
@@ -269,8 +275,8 @@ def read_sql_table(table_name, con, schema=None, index_col=None,
     con : SQLAlchemy engine
         Sqlite DBAPI connection mode not supported
     schema : string, default None
-        Name of SQL schema in database to query (if database flavor supports this).
-        If None, use default schema (default).
+        Name of SQL schema in database to query (if database flavor
+        supports this). If None, use default schema (default).
     index_col : string, optional
         Column to set as index
     coerce_float : boolean, default True
@@ -343,7 +349,7 @@ def read_sql_query(sql, con, index_col=None, coerce_float=True, params=None,
         decimal.Decimal) to floating point, useful for SQL result sets
     params : list, tuple or dict, optional
         List of parameters to pass to execute method.  The syntax used
-        to pass parameters is database driver dependent. Check your 
+        to pass parameters is database driver dependent. Check your
         database driver documentation for which of the five syntax styles,
         described in PEP 249's paramstyle, is supported.
         Eg. for psycopg2, uses %(name)s so use params={'name' : 'value'}
@@ -393,7 +399,7 @@ def read_sql(sql, con, index_col=None, coerce_float=True, params=None,
         decimal.Decimal) to floating point, useful for SQL result sets
     params : list, tuple or dict, optional
         List of parameters to pass to execute method.  The syntax used
-        to pass parameters is database driver dependent. Check your 
+        to pass parameters is database driver dependent. Check your
         database driver documentation for which of the five syntax styles,
         described in PEP 249's paramstyle, is supported.
         Eg. for psycopg2, uses %(name)s so use params={'name' : 'value'}
@@ -469,8 +475,8 @@ def to_sql(frame, name, con, flavor='sqlite', schema=None, if_exists='fail',
         'mysql' is deprecated and will be removed in future versions, but it
         will be further supported through SQLAlchemy engines.
     schema : string, default None
-        Name of SQL schema in database to write to (if database flavor supports
-        this). If None, use default schema (default).
+        Name of SQL schema in database to write to (if database flavor
+        supports this). If None, use default schema (default).
     if_exists : {'fail', 'replace', 'append'}, default 'fail'
         - fail: If table exists, do nothing.
         - replace: If table exists, drop it, recreate it, and insert data.
@@ -482,7 +488,7 @@ def to_sql(frame, name, con, flavor='sqlite', schema=None, if_exists='fail',
         `index` is True, then the index names are used.
         A sequence should be given if the DataFrame uses MultiIndex.
     chunksize : int, default None
-        If not None, then rows will be written in batches of this size at a 
+        If not None, then rows will be written in batches of this size at a
         time.  If None, all rows will be written at once.
 
     """
@@ -535,7 +541,9 @@ def has_table(table_name, con, flavor='sqlite', schema=None):
                   "and will be removed in future versions. "
                   "MySQL will be further supported with SQLAlchemy engines.")
 
-def pandasSQL_builder(con, flavor=None, schema=None, meta=None, is_cursor=False):
+
+def pandasSQL_builder(con, flavor=None, schema=None, meta=None,
+                      is_cursor=False):
     """
     Convenience function to return the correct PandasSQL subclass based on the
     provided parameters
@@ -622,7 +630,7 @@ def insert_data(self):
                     "duplicate name in index/columns: {0}".format(err))
         else:
             temp = self.frame
-        
+
         column_names = list(map(str, temp.columns))
         ncols = len(column_names)
         data_list = [None] * ncols
@@ -631,7 +639,8 @@ def insert_data(self):
         for i in range(len(blocks)):
             b = blocks[i]
             if b.is_datetime:
-                # convert to microsecond resolution so this yields datetime.datetime
+                # convert to microsecond resolution so this yields
+                # datetime.datetime
                 d = b.values.astype('M8[us]').astype(object)
             else:
                 d = np.array(b.values, dtype=object)
@@ -647,7 +656,7 @@ def insert_data(self):
         return column_names, data_list
 
     def _execute_insert(self, conn, keys, data_iter):
-        data = [dict( (k, v) for k, v in zip(keys, row) ) for row in data_iter]
+        data = [dict((k, v) for k, v in zip(keys, row)) for row in data_iter]
         conn.execute(self.insert_statement(), data)
 
     def insert(self, chunksize=None):
@@ -658,11 +667,11 @@ def insert(self, chunksize=None):
         if nrows == 0:
             return
 
-        if chunksize is None: 
+        if chunksize is None:
             chunksize = nrows
         elif chunksize == 0:
             raise ValueError('chunksize argument should be non-zero')
-            
+
         chunks = int(nrows / chunksize) + 1
 
         with self.pd_sql.run_transaction() as conn:
@@ -715,7 +724,8 @@ def _index_name(self, index, index_label):
                 else:
                     return index_label
             # return the used column labels for the index columns
-            if nlevels == 1 and 'index' not in self.frame.columns and self.frame.index.name is None:
+            if (nlevels == 1 and 'index' not in self.frame.columns
+                    and self.frame.index.name is None):
                 return ['index']
             else:
                 return [l if l is not None else "level_{0}".format(i)
@@ -739,7 +749,7 @@ def _get_column_names_and_types(self, dtype_mapper):
 
         column_names_and_types += [
             (str(self.frame.columns[i]),
-             dtype_mapper(self.frame.iloc[:,i]),
+             dtype_mapper(self.frame.iloc[:, i]),
              False)
             for i in range(len(self.frame.columns))
             ]
@@ -756,9 +766,8 @@ def _create_table_setup(self):
                    for name, typ, is_index in column_names_and_types]
 
         if self.keys is not None:
-            columns.append(PrimaryKeyConstraint(self.keys, 
-                             name=self.name+'_pk'))
-
+            pkc = PrimaryKeyConstraint(self.keys, name=self.name + '_pk')
+            columns.append(pkc)
 
         schema = self.schema or self.pd_sql.meta.schema
 
@@ -770,17 +779,16 @@ def _create_table_setup(self):
         return Table(self.name, meta, *columns, schema=schema)
 
     def _harmonize_columns(self, parse_dates=None):
-        """ Make a data_frame's column type align with an sql_table
-            column types
-            Need to work around limited NA value support.
-            Floats are always fine, ints must always
-            be floats if there are Null values.
-            Booleans are hard because converting bool column with None replaces
-            all Nones with false. Therefore only convert bool if there are no
-            NA values.
-            Datetimes should already be converted
-            to np.datetime if supported, but here we also force conversion
-            if required
+        """
+        Make the DataFrame's column types align with the SQL table
+        column types.
+        Need to work around limited NA value support. Floats are always
+        fine, ints must always be floats if there are Null values.
+        Booleans are hard because converting bool column with None replaces
+        all Nones with false. Therefore only convert bool if there are no
+        NA values.
+        Datetimes should already be converted to np.datetime64 if supported,
+        but here we also force conversion if required
         """
         # handle non-list entries for parse_dates gracefully
         if parse_dates is True or parse_dates is None or parse_dates is False:
@@ -823,7 +831,7 @@ def _harmonize_columns(self, parse_dates=None):
 
     def _sqlalchemy_type(self, col):
         from sqlalchemy.types import (BigInteger, Float, Text, Boolean,
-            DateTime, Date, Time, Interval)
+            DateTime, Date, Time)
 
         if com.is_datetime64_dtype(col):
             try:
@@ -874,12 +882,12 @@ class PandasSQL(PandasObject):
     """
 
     def read_sql(self, *args, **kwargs):
-        raise ValueError(
-            "PandasSQL must be created with an SQLAlchemy engine or connection+sql flavor")
+        raise ValueError("PandasSQL must be created with an SQLAlchemy engine"
+                         " or connection+sql flavor")
 
     def to_sql(self, *args, **kwargs):
-        raise ValueError(
-            "PandasSQL must be created with an SQLAlchemy engine or connection+sql flavor")
+        raise ValueError("PandasSQL must be created with an SQLAlchemy engine"
+                         " or connection+sql flavor")
 
 
 class PandasSQLAlchemy(PandasSQL):
@@ -897,7 +905,7 @@ def __init__(self, engine, schema=None, meta=None):
         self.meta = meta
 
     def run_transaction(self):
-       return self.engine.begin()
+        return self.engine.begin()
 
     def execute(self, *args, **kwargs):
         """Simple passthrough to SQLAlchemy engine"""
@@ -964,8 +972,8 @@ def drop_table(self, table_name, schema=None):
             self.meta.clear()
 
     def _create_sql_schema(self, frame, table_name, keys=None):
-        table = PandasSQLTable(table_name, self, frame=frame, index=False, 
-            keys=keys)
+        table = PandasSQLTable(table_name, self, frame=frame, index=False,
+                               keys=keys)
         return str(table.sql_schema())
 
 
@@ -1025,9 +1033,11 @@ def _create_sql_schema(self, frame, table_name, keys=None):
 
 
 class PandasSQLTableLegacy(PandasSQLTable):
-    """Patch the PandasSQLTable for legacy support.
-        Instead of a table variable just use the Create Table
-        statement"""
+    """
+    Patch the PandasSQLTable for legacy support.
+    Instead of a table variable just use the Create Table statement.
+    """
+
     def sql_schema(self):
         return str(";\n".join(self.table))
 
@@ -1058,11 +1068,11 @@ def _execute_insert(self, conn, keys, data_iter):
         conn.executemany(self.insert_statement(), data_list)
 
     def _create_table_setup(self):
-        """Return a list of SQL statement that create a table reflecting the 
+        """
+        Return a list of SQL statement that create a table reflecting the
         structure of a DataFrame.  The first entry will be a CREATE TABLE
         statement while the rest will be CREATE INDEX statements
         """
-
         column_names_and_types = \
             self._get_column_names_and_types(self._sql_type_name)
 
@@ -1159,15 +1169,15 @@ def execute(self, *args, **kwargs):
             else:
                 cur.execute(*args)
             return cur
-        except Exception as e:
+        except Exception as exc:
             try:
                 self.con.rollback()
             except Exception:  # pragma: no cover
-                ex = DatabaseError(
-                    "Execution failed on sql: %s\n%s\nunable to rollback" % (args[0], e))
+                ex = DatabaseError("Execution failed on sql: %s\n%s\nunable"
+                                   " to rollback" % (args[0], exc))
                 raise_with_traceback(ex)
 
-            ex = DatabaseError("Execution failed on sql '%s': %s" % (args[0], e))
+            ex = DatabaseError("Execution failed on sql '%s': %s" % (args[0], exc))
             raise_with_traceback(ex)
 
     def read_sql(self, sql, index_col=None, coerce_float=True, params=None,
@@ -1213,11 +1223,11 @@ def to_sql(self, frame, name, if_exists='fail', index=True,
             `index` is True, then the index names are used.
             A sequence should be given if the DataFrame uses MultiIndex.
         schema : string, default None
-            Ignored parameter included for compatability with SQLAlchemy version
-            of `to_sql`.
+            Ignored parameter included for compatability with SQLAlchemy
+            version of ``to_sql``.
         chunksize : int, default None
-            If not None, then rows will be written in batches of this size at a 
-            time.  If None, all rows will be written at once.
+            If not None, then rows will be written in batches of this
+            size at a time. If None, all rows will be written at once.
 
         """
         table = PandasSQLTableLegacy(
@@ -1243,8 +1253,8 @@ def drop_table(self, name, schema=None):
         self.execute(drop_sql)
 
     def _create_sql_schema(self, frame, table_name, keys=None):
-        table = PandasSQLTableLegacy(table_name, self, frame=frame, index=False,
-                                     keys=keys)
+        table = PandasSQLTableLegacy(table_name, self, frame=frame,
+                                     index=False, keys=keys)
         return str(table.sql_schema())