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- ASCII Tables (`astropy.io.ascii`)

# ASCII Tables (`astropy.io.ascii`)

## Introduction

`astropy.io.ascii` provides methods for reading and writing a wide range of ASCII data table formats via built-in Extension Reader Classes. The emphasis is on flexibility and convenience of use, although readers can optionally use a less flexible C-based engine for reading and writing for improved performance. This subpackage was originally developed as `asciitable`.

The following shows a few of the ASCII formats that are available, while the section on Supported formats contains the full list.

- `Basic`: basic table with customizable delimiters and header configurations

- `Cds`: CDS format table (also Vizier)

- `Daophot`: table from the IRAF DAOphot package

- `Ecsv`: ECSV Format for lossless round-trip of data tables (recommended)

- `FixedWidth`: table with fixed-width columns (see also Fixed-Width Gallery)

- `Ipac`: IPAC format table

- `HTML`: HTML format table contained in a <table> tag

- `Latex`: LaTeX table with datavalue in the `tabular` environment

- `Mrt`: AAS Machine-Readable Tables (MRT))

- `SExtractor`: SExtractor format table

The strength of `astropy.io.ascii` is the support for astronomy-specific formats (often with metadata) and specialized data types such as SkyCoord, Time, and Quantity. For reading or writing large data tables in a generic format such as CSV, using the Table - Pandas interface is an option to consider.

Note

It is strongly encouraged to use the functionality from `astropy.io.ascii` through a higher level interface in the Data Tables package. See Unified File Read/Write Interface for more details.

## Getting Started

### Reading Tables

The majority of commonly encountered ASCII tables can be read with the `read()` function. Assume you have a file named `sources.dat` with the following contents:

    obsid redshift  X      Y     object
    3102  0.32      4167  4085   Q1250+568-A
    877   0.22      4378  3892   "Source 82"

This table can be read with the following:

    >>> from astropy.io import ascii
    >>> data = ascii.read("sources.dat")
    >>> print(data)
    obsid redshift  X    Y      object
    ----- -------- ---- ---- -----------
     3102     0.32 4167 4085 Q1250+568-A
      877     0.22 4378 3892   Source 82

The first argument to the `read()` function can be the name of a file, a string representation of a table, or a list of table lines. The return value (`data` in this case) is a Table object.

By default, `read()` will try to guess the table format by trying all of the supported formats.

Warning

Guessing the file format is often slow for large files because the reader tries parsing the file with every allowed format until one succeeds. For large files it is recommended to disable guessing with `guess=False`.

If guessing the format does not work, as in the case for unusually formatted tables, you may need to give `astropy.io.ascii` additional hints about the format.

To specify specific data types for one or more columns, use the `converters` argument (see Converters for Specifying Dtype for details). For instance if the `obsid` is actually a string identifier (instead of an integer) you can read the table with the code below. This also illustrates using the preferred Table interface for reading:

    >>> from astropy.table import Table
    >>> sources = """
    ... target observatory obsid
    ... TW_Hya Chandra     22178
    ... MP_Mus XMM         0406030101"""
    >>> data = Table.read(sources, format='ascii', converters={'obsid': str})
    >>> data
    <Table length=2>
    target observatory   obsid
     str6      str7      str10
    ------ ----------- ----------
    TW_Hya     Chandra      22178
    MP_Mus         XMM 0406030101

### Writing Tables

The `write()` function provides a way to write a data table as a formatted ASCII table. Most of the input table Supported Formats for reading are also available for writing. This provides a great deal of flexibility in the format for writing.

The following shows how to write a formatted ASCII table using the `write()` function:

    >>> import numpy as np
    >>> from astropy.io import ascii
    >>> from astropy.table import Table
    >>> data = Table()
    >>> data['x'] = np.array([1, 2, 3], dtype=np.int32)
    >>> data['y'] = data['x'] ** 2
    >>> ascii.write(data, 'values.dat', overwrite=True)

The `values.dat` file will then contain:

    x y
    1 1
    2 4
    3 9

It is also possible and encouraged to use the write functionality from `astropy.io.ascii` through a higher level interface in the Data Tables package (see Unified File Read/Write Interface for more details). For example:

    >>> data.write('values.dat', format='ascii', overwrite=True)

Attention

ECSV is recommended

For a reproducible ASCII version of your table, we recommend using the ECSV Format. This stores all the table meta-data (in particular the column types and units) to a comment section at the beginning while maintaining compatibility with most plain CSV readers. It also allows storing richer data like `SkyCoord` or multidimensional or variable-length columns. ECSV is also supported in java by STIL and TOPCAT,

To write our simple example table to ECSV we use:

    >>> data.write('values.ecsv', overwrite=True)

The `.ecsv` extension is recognized and implies using ECSV (equivalent to `format='ascii.ecsv'`). The `values.ecsv` file will then contain:

    # %ECSV 1.0
    # ---
    # datatype:
    # - {name: x, datatype: int32}
    # - {name: y, datatype: int32}
    # schema: astropy-2.0
    x y
    1 1
    2 4
    3 9

## Supported Formats

A full list of the supported `format` values and corresponding format types for ASCII tables is given below. The `Write` column indicates which formats support write functionality, and the `Fast` column indicates which formats are compatible with the fast Cython/C engine for reading and writing.

Format | Write | Fast | Description
--- | --- | --- | ---
`aastex` | Yes |  | `AASTex`: AASTeX deluxetable used for AAS journals
`basic` | Yes | Yes | `Basic`: Basic table with custom delimiters
`cds` | Yes |  | `Cds`: CDS format table
`commented_header` | Yes | Yes | `CommentedHeader`: Column names in a commented line
`csv` | Yes | Yes | `Csv`: Basic table with comma-separated values
`daophot` |  |  | `Daophot`: IRAF DAOphot format table
`ecsv` | Yes |  | `Ecsv`: Enhanced CSV format (recommended)
`fixed_width` | Yes |  | `FixedWidth`: Fixed width
`fixed_width_no_header` | Yes |  | `FixedWidthNoHeader`: Fixed-width with no header
`fixed_width_two_line` | Yes |  | `FixedWidthTwoLine`: Fixed-width with second header line
`html` | Yes |  | `HTML`: HTML format table
`ipac` | Yes |  | `Ipac`: IPAC format table
`latex` | Yes |  | `Latex`: LaTeX table
`mrt` | Yes |  | `Mrt`: AAS Machine-Readable Table format
`no_header` | Yes | Yes | `NoHeader`: Basic table with no headers
`qdp` | Yes |  | `QDP`: Quick and Dandy Plotter files
`rdb` | Yes | Yes | `Rdb`: Tab-separated with a type definition header line
`rst` | Yes |  | `RST`: reStructuredText simple format table
`sextractor` |  |  | `SExtractor`: SExtractor format table
`tab` | Yes | Yes | `Tab`: Basic table with tab-separated values

## Using `astropy.io.ascii`

The details of using `astropy.io.ascii` are provided in the following sections:

### Reading tables

- Reading Tables
  - Parameters for `read()`
  - Specifying Header and Data Location
  - Bad or Missing Values
  - Guess Table Format
  - Comments and Metadata
  - Converters for Specifying Dtype
  - Fortran-Style Exponents
  - Advanced Customization
  - Reading Large Tables in Chunks
  - How to Find and Fix Problems Reading a Table

### Writing tables

- Writing Tables
  - Examples
  - Parameters for `write()`
  - Machine-Readable Table Format

### ECSV Format

- ECSV Format
  - Usage
  - Simple Table
  - Masked Data
  - Mixin Columns
  - Multidimensional Columns
  - Variable-length arrays
  - Object arrays

### Fixed-Width Gallery

- Fixed-Width Gallery
  - Reading
  - Writing
  - Custom Header Rows

### Fast ASCII Engine

- Fast ASCII I/O
  - Examples
  - Parallel and Fast Conversion Options
  - Fast Converter
  - Reading Large Tables

### Base Class Elements

- Base Class Elements

### Extension Reader Classes

- Extension Reader Classes

## Performance Tips

By default, when trying to read a file the reader will guess the format, which involves trying to read it with many different readers. For better performance when dealing with large tables, it is recommended to specify the format and any options explicitly, and turn off guessing as well.

### Example

If you are reading a simple CSV file with a one-line header with column names, the following:

    read('example.csv', format='basic', delimiter=',', guess=False)  # doctest: +SKIP

can be at least an order of magnitude faster than:

    read('example.csv')  # doctest: +SKIP

## Reference/API

### astropy.io.ascii Package

An extensible ASCII table reader and writer.

#### Functions

`convert_numpy`(numpy_type) | Return a tuple containing a function which converts a list into a numpy array and the type produced by the converter function.
`get_read_trace`() | Return a traceback of the attempted read formats for the last call to `read` where guessing was enabled.
`get_reader`([Reader, Inputter, Outputter]) | Initialize a table reader allowing for common customizations.
`get_writer`([Writer, fast_writer]) | Initialize a table writer allowing for common customizations.
`read`(table[, guess]) | Read the input `table` and return the table.
`set_guess`(guess) | Set the default value of the `guess` parameter for read()
`write`(table[, output, format, Writer, ...]) | Write the input `table` to `filename`.

#### Classes

`AASTex`(**kwargs) | AASTeX format table.
`AllType`() | Subclass of all other data types.
`BaseData`() | Base table data reader.
`BaseHeader`() | Base table header reader
`BaseInputter`() | Get the lines from the table input and return a list of lines.
`BaseOutputter`() | Output table as a dict of column objects keyed on column name.
`BaseReader`() | Class providing methods to read and write an ASCII table using the specified header, data, inputter, and outputter instances.
`BaseSplitter`() | Base splitter that uses python's split method to do the work.
`Basic`() | Character-delimited table with a single header line at the top.
`BasicData`() | Basic table Data Reader
`BasicHeader`() | Basic table Header Reader
`Cds`([readme]) | CDS format table.
`Column`(name) | Table column.
`CommentedHeader`() | Character-delimited table with column names in a comment line.
`ContinuationLinesInputter`() | Inputter where lines ending in `continuation_char` are joined with the subsequent line. Example::.
`Csv`() | CSV (comma-separated-values) table.
`Daophot`() | DAOphot format table.
`DefaultSplitter`() | Default class to split strings into columns using python csv.
`Ecsv`() | ECSV (Enhanced Character Separated Values) format table.
`FastBasic`([default_kwargs]) | This class is intended to handle the same format addressed by the ordinary `Basic` writer, but it acts as a wrapper for underlying C code and is therefore much faster.
`FastCommentedHeader`(**kwargs) | A faster version of the `CommentedHeader` reader, which looks for column names in a commented line.
`FastCsv`(**kwargs) | A faster version of the ordinary `Csv` writer that uses the optimized C parsing engine.
`FastNoHeader`(**kwargs) | This class uses the fast C engine to read tables with no header line.
`FastRdb`(**kwargs) | A faster version of the `Rdb` reader.
`FastTab`(**kwargs) | A faster version of the ordinary `Tab` reader that uses the optimized C parsing engine.
`FixedWidth`([col_starts, col_ends, ...]) | Fixed width table with single header line defining column names and positions.
`FixedWidthData`() | Base table data reader.
`FixedWidthHeader`() | Fixed width table header reader.
`FixedWidthNoHeader`([col_starts, col_ends, ...]) | Fixed width table which has no header line.
`FixedWidthSplitter`() | Split line based on fixed start and end positions for each `col` in `self.cols`.
`FixedWidthTwoLine`([position_line, ...]) | Fixed width table which has two header lines.
`FloatType`() | Describes floating-point data.
`HTML`([htmldict]) | HTML format table.
`InconsistentTableError` | Indicates that an input table is inconsistent in some way.
`IntType`() | Describes integer data.
`Ipac`([definition, DBMS]) | IPAC format table.
`Latex`([ignore_latex_commands, latexdict, ...]) | LaTeX format table.
`Mrt`() | AAS MRT (Machine-Readable Table) format table.
`NoHeader`() | Character-delimited table with no header line.
`NoType`() | Superclass for `StrType` and `NumType` classes.
`NumType`() | Indicates that a column consists of numerical data.
`ParameterError` | Indicates that a reader cannot handle a passed parameter.
`QDP`([table_id, names, err_specs, sep]) | Quick and Dandy Plot table.
`RST`() | reStructuredText simple format table.
`Rdb`() | Tab-separated file with an extra line after the column definition line that specifies either numeric (N) or string (S) data.
`SExtractor`() | SExtractor format table.
`StrType`() | Indicates that a column consists of text data.
`Tab`() | Tab-separated table.
`TableOutputter`() | Output the table as an astropy.table.Table object.
`WhitespaceSplitter`() |

#### Class Inheritance Diagram