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# Fixed-Width Gallery

Fixed-width tables are those where each column has the same width for every row in the table. This is commonly used to make tables easy to read for humans or Fortran codes. It also reduces issues with quoting and special characters, for example:

    Col1   Col2    Col3 Col4
    ---- --------- ---- ----
     1.2   "hello"    1    a
     2.4 's worlds    2    2

There are a number of common variations in the formatting of fixed-width tables which `astropy.io.ascii` can read and write. The most significant difference is whether there is no header line (`FixedWidthNoHeader`), one header line (`FixedWidth`), or two header lines (`FixedWidthTwoLine`). Next, there are variations in the delimiter character, like whether the delimiter appears on either end (“bookends”), or if there is padding around the delimiter.

Details are available in the class API documentation, but the easiest way to understand all of the options and their interactions is by example.

## Reading

### Fixed Width

Nice, typical, fixed-format table:

    >>> from astropy.io import ascii
    >>> table = """
    ... # comment (with blank line above)
    ... |  Col1  |  Col2   |
    ... |  1.2   | "hello" |
    ... |  2.4   |'s worlds|
    ... """
    >>> ascii.read(table, format='fixed_width')
    <Table length=2>
      Col1     Col2
    float64    str9
    ------- ---------
        1.2   "hello"
        2.4 's worlds

Typical fixed-format table with col names provided:

    >>> table = """
    ... # comment (with blank line above)
    ... |  Col1  |  Col2   |
    ... |  1.2   | "hello" |
    ... |  2.4   |'s worlds|
    ... """
    >>> ascii.read(table, format='fixed_width', names=['name1', 'name2'])
    <Table length=2>
     name1    name2
    float64    str9
    ------- ---------
        1.2   "hello"
        2.4 's worlds

Weird input table with data values chopped by col extent:

    >>> table = """
    ...   Col1  |  Col2 |
    ...   1.2       "hello"
    ...   2.4   sdf's worlds
    ... """
    >>> ascii.read(table, format='fixed_width')
    <Table length=2>
      Col1    Col2
    float64   str7
    ------- -------
        1.2    "hel
        2.4 df's wo

Table with double delimiters:

    >>> table = """
    ... || Name ||   Phone ||         TCP||
    ... |  John  | 555-1234 |192.168.1.10X|
    ... |  Mary  | 555-2134 |192.168.1.12X|
    ... |   Bob  | 555-4527 | 192.168.1.9X|
    ... """
    >>> ascii.read(table, format='fixed_width')
    <Table length=3>
    Name  Phone       TCP
    str4   str8      str12
    ---- -------- ------------
    John 555-1234 192.168.1.10
    Mary 555-2134 192.168.1.12
     Bob 555-4527  192.168.1.9

Table with space delimiter:

    >>> table = """
    ...  Name  --Phone-    ----TCP-----
    ...  John  555-1234    192.168.1.10
    ...  Mary  555-2134    192.168.1.12
    ...   Bob  555-4527     192.168.1.9
    ... """
    >>> ascii.read(table, format='fixed_width', delimiter=' ')
    <Table length=3>
    Name --Phone- ----TCP-----
    str4   str8      str12
    ---- -------- ------------
    John 555-1234 192.168.1.10
    Mary 555-2134 192.168.1.12
     Bob 555-4527  192.168.1.9

Table with no header row and auto-column naming:

Use `header_start` and `data_start` keywords to indicate no header line.

    >>> table = """
    ... |  John  | 555-1234 |192.168.1.10|
    ... |  Mary  | 555-2134 |192.168.1.12|
    ... |   Bob  | 555-4527 | 192.168.1.9|
    ... """
    >>> ascii.read(table, format='fixed_width',
    ...            header_start=None, data_start=0)
    <Table length=3>
    col1   col2       col3
    str4   str8      str12
    ---- -------- ------------
    John 555-1234 192.168.1.10
    Mary 555-2134 192.168.1.12
     Bob 555-4527  192.168.1.9

Table with no header row and with col names provided:

Second and third rows also have hanging spaces after final “|”. Use header_start and data_start keywords to indicate no header line.

    >>> table = ["|  John  | 555-1234 |192.168.1.10|",
    ...          "|  Mary  | 555-2134 |192.168.1.12|  ",
    ...          "|   Bob  | 555-4527 | 192.168.1.9|  "]
    >>> ascii.read(table, format='fixed_width',
    ...            header_start=None, data_start=0,
    ...            names=('Name', 'Phone', 'TCP'))
    <Table length=3>
    Name  Phone       TCP
    str4   str8      str12
    ---- -------- ------------
    John 555-1234 192.168.1.10
    Mary 555-2134 192.168.1.12
     Bob 555-4527  192.168.1.9

### Fixed Width No Header

Table with no header row and auto-column naming. Use the ``fixed_width_no_header`` format for convenience:

    >>> table = """
    ... |  John  | 555-1234 |192.168.1.10|
    ... |  Mary  | 555-2134 |192.168.1.12|
    ... |   Bob  | 555-4527 | 192.168.1.9|
    ... """
    >>> ascii.read(table, format='fixed_width_no_header')
    <Table length=3>
    col1   col2       col3
    str4   str8      str12
    ---- -------- ------------
    John 555-1234 192.168.1.10
    Mary 555-2134 192.168.1.12
     Bob 555-4527  192.168.1.9

Table with no delimiter with column start and end values specified:

This uses the col_starts and col_ends keywords. Note that the col_ends values are inclusive so a position range of zero to five will select the first six characters.

    >>> table = """
    ... #    5   9     17  18      28    <== Column start / end indexes
    ... #    |   |       ||         |    <== Column separation positions
    ...   John   555- 1234 192.168.1.10
    ...   Mary   555- 2134 192.168.1.12
    ...    Bob   555- 4527  192.168.1.9
    ... """
    >>> ascii.read(table, format='fixed_width_no_header',
    ...                 names=('Name', 'Phone', 'TCP'),
    ...                 col_starts=(0, 9, 18),
    ...                 col_ends=(5, 17, 28),
    ...                 )
    <Table length=3>
    Name   Phone      TCP
    str4    str9     str10
    ---- --------- ----------
    John 555- 1234 192.168.1.
    Mary 555- 2134 192.168.1.
     Bob 555- 4527  192.168.1

Table with no delimiter with only column start or end values specified:

If only the col_starts keyword is given, it is assumed that each column ends where the next column starts, and the final column ends at the same position as the longest line of data.

Conversely, if only the col_ends keyword is given, it is assumed that the first column starts at position zero and that each successive column starts immediately after the previous one.

The two examples below read the same table and produce the same result.

    >>> table = """
    ... #1       9        19                <== Column start indexes
    ... #|       |         |                <== Column start positions
    ... #<------><--------><------------->  <== Inferred column positions
    ...   John   555- 1234 192.168.1.10
    ...   Mary   555- 2134 192.168.1.123
    ...    Bob   555- 4527  192.168.1.9
    ...    Bill  555-9875  192.255.255.255
    ... """
    >>> ascii.read(table,
    ...                 format='fixed_width_no_header',
    ...                 names=('Name', 'Phone', 'TCP'),
    ...                 col_starts=(1, 9, 19),
    ...                 )
    <Table length=4>
    Name   Phone         TCP
    str4    str9        str15
    ---- --------- ---------------
    John 555- 1234    192.168.1.10
    Mary 555- 2134   192.168.1.123
     Bob 555- 4527     192.168.1.9
    Bill  555-9875 192.255.255.255

    >>> ascii.read(table,
    ...                 format='fixed_width_no_header',
    ...                 names=('Name', 'Phone', 'TCP'),
    ...                 col_ends=(8, 18, 32),
    ...                 )
    <Table length=4>
    Name   Phone        TCP
    str4    str9       str14
    ---- --------- --------------
    John 555- 1234   192.168.1.10
    Mary 555- 2134  192.168.1.123
     Bob 555- 4527    192.168.1.9
    Bill  555-9875 192.255.255.25

### Fixed Width Two Line

Typical fixed-format table with two header lines with some cruft:

    >>> table = """
    ...   Col1    Col2
    ...   ----  ---------
    ...    1.2xx"hello"
    ...   2.4   's worlds
    ... """
    >>> ascii.read(table, format='fixed_width_two_line')
    <Table length=2>
      Col1     Col2
    float64    str9
    ------- ---------
        1.2   "hello"
        2.4 's worlds

reStructuredText table:

    >>> table = """
    ... ======= ===========
    ...   Col1    Col2
    ... ======= ===========
    ...   1.2   "hello"
    ...   2.4   's worlds
    ... ======= ===========
    ... """
    >>> ascii.read(table, format='fixed_width_two_line',
    ...                 header_start=1, position_line=2, data_end=-1)
    <Table length=2>
      Col1     Col2
    float64    str9
    ------- ---------
        1.2   "hello"
        2.4 's worlds

Text table designed for humans and test having position line before the header line:

    >>> table = """
    ... +------+----------+
    ... | Col1 |   Col2   |
    ... +------|----------+
    ... |  1.2 | "hello"  |
    ... |  2.4 | 's worlds|
    ... +------+----------+
    ... """
    >>> ascii.read(table, format='fixed_width_two_line', delimiter='+',
    ...                 header_start=1, position_line=0, data_start=3, data_end=-1)
    <Table length=2>
      Col1     Col2
    float64    str9
    ------- ---------
        1.2   "hello"
        2.4 's worlds

## Writing

### Fixed Width

Define input values ``dat`` for all write examples:

    >>> table = """
    ... | Col1 |  Col2     |  Col3 | Col4 |
    ... | 1.2  | "hello"   |  1    | a    |
    ... | 2.4  | 's worlds |  2    | 2    |
    ... """
    >>> dat = ascii.read(table, format='fixed_width')

Write a table as a normal fixed-width table:

    >>> ascii.write(dat, format='fixed_width')
    | Col1 |      Col2 | Col3 | Col4 |
    |  1.2 |   "hello" |    1 |    a |
    |  2.4 | 's worlds |    2 |    2 |

Write a table as a fixed-width table with no padding:

    >>> ascii.write(dat, format='fixed_width', delimiter_pad=None)
    |Col1|     Col2|Col3|Col4|
    | 1.2|  "hello"|   1|   a|
    | 2.4|'s worlds|   2|   2|

Write a table as a fixed-width table with no bookend:

    >>> ascii.write(dat, format='fixed_width', bookend=False)
    Col1 |      Col2 | Col3 | Col4
     1.2 |   "hello" |    1 |    a
     2.4 | 's worlds |    2 |    2

Write a table as a fixed-width table with no delimiter:

    >>> ascii.write(dat, format='fixed_width', bookend=False, delimiter=None)
    Col1       Col2  Col3  Col4
     1.2    "hello"     1     a
     2.4  's worlds     2     2

Write a table as a fixed-width table with no delimiter and formatting:

    >>> ascii.write(dat, format='fixed_width',
    ...                  formats={'Col1': '%-8.3f', 'Col2': '%-15s'})
    |     Col1 |            Col2 | Col3 | Col4 |
    | 1.200    | "hello"         |    1 |    a |
    | 2.400    | 's worlds       |    2 |    2 |

### Fixed Width No Header

Write a table as a normal fixed-width table:

    >>> ascii.write(dat, format='fixed_width_no_header')
    | 1.2 |   "hello" | 1 | a |
    | 2.4 | 's worlds | 2 | 2 |

Write a table as a fixed-width table with no padding:

    >>> ascii.write(dat, format='fixed_width_no_header', delimiter_pad=None)
    |1.2|  "hello"|1|a|
    |2.4|'s worlds|2|2|

Write a table as a fixed-width table with no bookend:

    >>> ascii.write(dat, format='fixed_width_no_header', bookend=False)
    1.2 |   "hello" | 1 | a
    2.4 | 's worlds | 2 | 2

Write a table as a fixed-width table with no delimiter:

    >>> ascii.write(dat, format='fixed_width_no_header', bookend=False,
    ...                  delimiter=None)
    1.2    "hello"  1  a
    2.4  's worlds  2  2

### Fixed Width Two Line

Write a table as a normal fixed-width table:

    >>> ascii.write(dat, format='fixed_width_two_line')
    Col1      Col2 Col3 Col4
    ---- --------- ---- ----
     1.2   "hello"    1    a
     2.4 's worlds    2    2

Write a table as a fixed width table with space padding and ‘=’ position_char:

    >>> ascii.write(dat, format='fixed_width_two_line',
    ...                  delimiter_pad=' ', position_char='=')
    Col1        Col2   Col3   Col4
    ====   =========   ====   ====
     1.2     "hello"      1      a
     2.4   's worlds      2      2

Write a table as a fixed-width table with no bookend:

    >>> ascii.write(dat, format='fixed_width_two_line', bookend=True, delimiter='|')
    |Col1|     Col2|Col3|Col4|
    |----|---------|----|----|
    | 1.2|  "hello"|   1|   a|
    | 2.4|'s worlds|   2|   2|

## Custom Header Rows

The `fixed_width`, `fixed_width_two_line`, and `rst` formats normally include a single row with the column names in the header. However, for these formats you can customize the column attributes which appear as header rows. The available column attributes are `name`, `dtype`, `format`, `description` and `unit`. This is done by listing the desired the header rows using the `header_rows` keyword argument.

::

      >>> from astropy.table.table_helpers import simple_table
      >>> dat = simple_table(size=3, cols=4)
      >>> dat["a"].info.unit = "m"
      >>> dat["d"].info.unit = "m/s"
      >>> dat["b"].info.format = ".2f"
      >>> dat["c"].info.description = "C column"
      >>> ascii.write(
      ...    dat,
      ...    format="fixed_width",
      ...    header_rows=["name", "unit", "format", "description"],
      ... )
      |     a |       b |        c |     d |
      |     m |         |          | m / s |
      |       |     .2f |          |       |
      |       |         | C column |       |
      |     1 |    1.00 |        c |     4 |
      |     2 |    2.00 |        d |     5 |
      |     3 |    3.00 |        e |     6 |

In this example the 1st row is the `name`, the 2nd row is the `unit`, and so forth. You must supply the `name` value in the `header_rows` list in order to get an output with the column name included.

A table with non-standard header rows can be read back in the same way, using the same list of `header_rows`:

    >>> txt = """\
    ... | int32 | float32 |      <U4 | uint8 |
    ... |     a |       b |        c |     d |
    ... |     m |         |          | m / s |
    ... |       |     .2f |          |       |
    ... |       |         | C column |       |
    ... |     1 |    1.00 |        c |     4 |
    ... |     2 |    2.00 |        d |     5 |
    ... |     3 |    3.00 |        e |     6 |
    ... """
    >>> dat = ascii.read(
    ...     txt,
    ...     format="fixed_width",
    ...     header_rows=["dtype", "name", "unit", "format", "description"],
    ... )
    >>> dat.info
    <Table length=3>
    name  dtype   unit format description
    ---- ------- ----- ------ -----------
    a   int32     m
    b float32          .2f
    c    str4                 C column
    d   uint8 m / s

The same idea can be used with the `fixed_width_two_line` format:

    >>> txt = """\
    ...     a       b        c     d
    ... int64 float64      <U1 int64
    ...     m                  m / s
    ... ----- ------- -------- -----
    ...     1    1.00        c     4
    ...     2    2.00        d     5
    ...     3    3.00        e     6
    ... """
    >>> dat = ascii.read(
    ...     txt,
    ...     format="fixed_width_two_line",
    ...     header_rows=["name", "dtype", "unit"],
    ... )
    >>> dat
    <Table length=3>
      a      b     c     d
      m                m / s
    int64 float64 str1 int64
    ----- ------- ---- -----
        1     1.0    c     4
        2     2.0    d     5
        3     3.0    e     6

Note that the `two_line` in the `fixed_width_two_line` format name refers to the default situation where the header consists two lines, a row of column names and a row of separator lines. This is a bit of a misnomer when using `header_rows`.