Source code for parsons.etl.table

from parsons.etl.etl import ETL
from parsons.etl.tofrom import ToFrom
from parsons.utilities import files
import petl
import pickle
import logging

logger = logging.getLogger(__name__)


[docs]class Table(ETL, ToFrom): """ Create a Parsons Table. Accepts one of the following: - A list of lists, with list[0] holding field names, and the other lists holding data - A list of dicts - A petl table `Args:` lst: list See above for accepted list formats source: str The original data source from which the data was pulled (optional) name: str The name of the table (optional) """ def __init__(self, lst=[]): self.table = None lst_type = type(lst) if lst_type in [list, tuple]: # Check for empty list if not len(lst): self.table = petl.fromdicts([]) else: row_type = type(lst[0]) # Check for list of dicts if row_type == dict: self.table = petl.fromdicts(lst) # Check for list of lists elif row_type in [list, tuple]: self.table = petl.wrap(lst) else: # Create from a petl table self.table = lst if not self.is_valid_table(): raise ValueError("Could not create Table") # Count how many times someone is indexing directly into this table, so we can warn # against inefficient usage. self._index_count = 0 def __repr__(self): return repr(petl.dicts(self.table)) def __iter__(self): return iter(petl.dicts(self.table)) def __getitem__(self, index): if isinstance(index, int): return self.row_data(index) elif isinstance(index, str): return self.column_data(index) elif isinstance(index, slice): tblslice = petl.rowslice(self.table, index.start, index.stop, index.step) return [row for row in tblslice] else: raise TypeError("You must pass a string or an index as a value.") def __bool__(self): # Try to get a single row from our table head_one = petl.head(self.table) # See if our single row is empty return petl.nrows(head_one) > 0 def _repr_html_(self): """ Leverage Petl functionality to display well formatted tables in Jupyter Notebook. """ return self.table._repr_html_() @property def num_rows(self): """ `Returns:` int Number of rows in the table """ return petl.nrows(self.table) @property def data(self): """ Returns an iterable object for iterating over the raw data rows as tuples (without field names) """ return @property def columns(self): """ `Returns:` list List of the table's column names """ return list(petl.header(self.table)) @property def first(self): """ Returns the first value in the table. Useful for database queries that only return a single value. """ try: return[0][0] # If first value is empty, return None except IndexError: return None def row_data(self, row_index): """ Returns a row in table `Args:` row_index: int `Returns:` dict A dictionary of the row with the column as the key and the cell as the value. """ self._index_count += 1 if self._index_count >= DIRECT_INDEX_WARNING_COUNT: logger.warning( """ You have indexed directly into this Table multiple times. This can be inefficient, as data transformations you've made will be computed _each time_ you index into the Table. If you are accessing many rows of data, consider switching to this style of iteration, which is much more efficient: `for row in table:` """ ) return petl.dicts(self.table)[row_index] def column_data(self, column_name): """ Returns the data in the column as a list. `Args:` column_name: str The name of the column `Returns`: list A list of data in the column. """ if column_name in self.columns: return list(self.table[column_name]) else: raise ValueError("Column name not found.")
[docs] def materialize(self): """ "Materializes" a Table, meaning all data is loaded into memory and all pending transformations are applied. Use this if petl's lazy-loading behavior is causing you problems, eg. if you want to read data from a file immediately. """ self.table = petl.wrap(petl.tupleoftuples(self.table))
[docs] def materialize_to_file(self, file_path=None): """ "Materializes" a Table, meaning all pending transformations are applied. Unlike the original materialize function, this method does not bring the data into memory, but instead loads the data into a local temp file. This method updates the current table in place. `Args:` file_path: str The path to the file to materialize the table to; if not specified, a temp file will be created. `Returns:` str Path to the temp file that now contains the table """ # Load the data in batches, and "pickle" the rows to a temp file. # (We pickle rather than writing to, say, a CSV, so that we maintain # all the type information for each field.) file_path = file_path or files.create_temp_file() with open(file_path, "wb") as handle: for row in self.table: pickle.dump(list(row), handle) # Load a Table from the file self.table = petl.frompickle(file_path) return file_path
def is_valid_table(self): """ Performs some simple checks on a Table. Specifically, verifies that we have a valid petl table within the Parsons Table. `Returns:` bool """ if not self.table: return False try: self.columns except StopIteration: return False return True def empty_column(self, column): """ Checks if a given column is empty. Returns ``True`` if empty and ``False`` if not empty. `Args:` column: str The column name `Returns:` bool """ if petl.nrows(petl.selectnotnone(self.table, column)) == 0: return True else: return False