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get_reader() returns csv.reader-like objects from multiple sources

Project description

get-reader

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This module provides a get_reader() function that returns reader objects similar to those returned by csv.reader(). This package:

  • reduces common boilerplate code for handling files and reading records

  • reads data from CSV, pandas, SQL connections, MS Excel, DBF, and squint

  • provides a single interface across Python versions (including seamless Unicode-aware CSV support for Python 2)

  • is easy to incorporate into your own projects:

    • has no hard dependencies
    • runs on Python 2.6, 2.7, 3.2 through 3.8, PyPy, PyPy3, and Jython
    • is freely available under the Apache License, version 2
    • can be easily vendored directly into your codebase if you don't want to include it as a dependency

Open a UTF-8 encoded CSV:

from get_reader import get_reader

reader = get_reader('myfile.csv')

for row in reader:
    print(', '.join(row))

In the above example, file handling is managed automatically by the reader object. The file is automatically closed when the iterator is exhausted or when the object is deleted. It also handles Unicode in Python 2 without changes.

Open a Latin-1 (ISO-8859-1) encoded CSV file:

reader = get_reader('myfile.csv', encoding='latin-1')

for row in reader:
    print(', '.join(row))

Use the reader as a context manager:

with get_reader('myfile.csv') as reader:
    for row in reader:
        print(', '.join(row))

In this example, reader automatically closes its internal file object when exiting the with block even if the for-loop doesn't finish exhausting the reader.

Access other data sources:

# From a pandas DataFrame, Series, Index, or MultiIndex.
df = pd.DataFrame([...])
reader = get_reader(df)  # requires pandas

# From a database connection.
connection = ...
reader = get_reader(connection, 'SELECT col1, col2 FROM mytable;')

# From an Excel file--must install with 'excel' option.
reader = get_reader('myfile.xlsx')

# From a DBF file--must install with 'dbf' option.
reader = get_reader('myfile.dbf')

# From a squint Select, Query, or Result.
select = ...
reader = get_reader(select({'col1': 'col2'}).sum())

Call constructors directly to override auto-detect behavior:

# Specify tab-delimited data from a text file.
reader = get_reader.from_csv('myfile.dat', delimiter='\t')

Install

The get_reader module has no hard dependencies; is tested on Python 2.6, 2.7, 3.2 through 3.8, PyPy, PyPy3, and Jython; and is freely available under the Apache License, version 2.

You can install get_reader using pip:

pip install get_reader

To install optional support for MS Excel and DBF files (dBase, Foxpro, etc.), use the following:

pip install get_reader[excel,dbf]

Python 2 Support Statement

While official support for Python 2 ends on January 1, 2020, this project will continue to support older versions as long as the existing ecosystem provides the ability to run automated tests on those older versions.

Reference

get_reader(obj, *args, **kwds)

Return a Reader object which will iterate over records in the given obj—like a csv.reader(). The given obj may be one of the following:

  • CSV file (string path or file object)
  • iterable of dictionary rows
  • database connection (should be DBAPI2 compatible)
  • pandas DataFrame, Series, Index, or MultiIndex
  • squint Select, Query, or Result

If optional extras are installed, obj may also be:

  • MS Excel file path
  • DBF file path

When obj is a file path, the Reader contains a file object that is handled internally. When given a file-like obj (rather than a path), users are responsible for properly closing this file themselves.

The given obj is checked against supported types and automatically passed to the appropriate constructor if a match is found. If obj is a string, it is treated as a file path whose extension determines its content type. Any *args and **kwds are passed along to the matching constructor:

from get_reader import get_reader

# CSV file.
reader = get_reader('myfile.csv')

# Database connection.
connection = ...
reader = get_reader(connection, 'SELECT col1, col2 FROM mytable;')

# Pandas DataFrame.
df = pd.DataFrame([...])
reader = get_reader(df)

# Excel file.
reader = get_reader('myfile.xlsx', worksheet='Sheet2')

If the obj type cannot be determined automatically, users can call the constructor methods directly.

Constructor Methods

get_reader.from_csv(csvfile, encoding='utf-8', dialect='excel', **kwds)

Return a reader object which will iterate over lines in the given csvfile. The csvfile can be a string (treated as a file path) or any object which supports the iterator protocol and returns a string each time its __next__() method is called—file objects and list objects are both suitable. If csvfile is a file object, it should be opened with newline=''.

from get_reader import get_reader

reader = get_reader.from_csv('myfile.tab', delimiter='\t')

Using explicit file handling:

from get_reader import get_reader

with open('myfile.csv') as csvfile:
    reader = get_reader.from_csv(fh)

get_reader.from_dicts(records, fieldnames=None)

Return a reader object which will iterate over the given dictionary records. This can be thought of as converting a csv.DictReader() into a plain, non-dictionary csv.reader().

from get_reader import get_reader

dictrows = [
    {'A': 1, 'B': 'x'},
    {'A': 2, 'B': 'y'},
]

reader = get_reader.from_dicts(dictrows)

This method assumes that record contents are consistent. If the first record is a dictionary, it is assumed that all following records will be dictionaries with matching keys.

get_reader.from_sql(connection, table_or_query)

Return a reader object which will iterate over the records from a given database table or over the records returned from a SQL query. The connection should be a DBAPI2 compatible database connection and table_or_query must be a string with a table name or a SQL query.

Read records from a specified table:

from get_reader import get_reader

connection = ...
reader = get_reader.from_sql(connection, 'mytable')

Read records from the results of a SQL query:

reader = get_reader.from_sql(connection, 'SELECT col1, col2 FROM mytable;')

get_reader.from_excel(path, worksheet=0)

Return a reader object which will iterate over lines in the given Excel worksheet. The path must specify an XLSX or XLS file and worksheet must specify the index or name of the worksheet to load (defaults to the first worksheet).

Load first worksheet:

from get_reader import get_reader

reader = get_reader.from_excel('mydata.xlsx')

Specific worksheets can be loaded by name (a string) or index (an integer):

reader = get_reader.from_excel('mydata.xlsx', 'Sheet 2')

get_reader.from_pandas(obj, index=True)

Return a reader object which will iterate over records in a pandas DataFrame, Series, Index or MultiIndex.

import pandas as pd
from get_reader import get_reader

df = pd.DataFrame(...)
reader = get_reader.from_pandas(df)

get_reader.from_dbf(filename, encoding=None, **kwds)

Return a reader object which will iterate over lines in the given DBF file (from dBase, FoxPro, etc.).

from get_reader import get_reader

reader = get_reader.from_dbf('myfile.dbf')

get_reader.from_squint(obj, fieldnames=None)

Return a reader object which will iterate over the records returned from a squint Select, Query, or Result. If the fieldnames argument is not provided, this function tries to construct names using the values from the underlying object.

import squint
from get_reader import get_reader

select = squint.Select(...)
reader = get_reader.from_squint(select)

class Reader(iterable, closefunc=<no value>)

An iterator which will produce rows from the given iterable. The given iterable should produce non-string sequences. An optional closefunc may be provided to close associated resources (files, database cursors, etc.) once the reader is no longer needed—it will be automatically called when:

  • the iterable is exhausted
  • exiting a with statement (if used as a context manager)
  • the Reader is garbage collected

Reader.close()

Closes any associated resources (calls closefunc early):

from get_reader import Reader

reader = Reader(..., closefunc=...)
reader.close()  # <- Explicitly close resources.

If the resources have already been closed, this method passes without error.

class ReaderLike()

An abstract class that can be used for type checking. Objects will test as ReaderLike if they are one of the following:

  • instance of the Reader class
  • object returned by csv.reader()
  • non-exhaustible iterable that produces non-string sequences

See the following examples:

>>> isinstance(get_reader(csvfile), ReaderLike)
True

>>> isinstance(csv.reader(csvfile), ReaderLike)
True

>>> list_of_lists = [['col1', 'col2'], ['a', 'b']]
>>> isinstance(list_of_lists, ReaderLike)
True

>>> list_of_strings = ['col1,col2', 'a,b']
>>> isinstance(list_of_strings, ReaderLike)
False

>>> list_of_sets = [{'col1', 'col2'}, {'a', 'b'}]
>>> isinstance(list_of_sets, ReaderLike)
False

Freely licensed under the Apache License, Version 2.0

(C) Copyright 2018 – 2019 Shawn Brown.

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