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 signicant 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, whether the delimiter appears on either end (“bookends”), and padding around the delimiter.

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

Reading

FixedWidth

Nice, typical fixed format table

>>> import astropy.io.ascii
>>> table = """
... # comment (with blank line above)
... |  Col1  |  Col2   |
... |  1.2   | "hello" |
... |  2.4   |'s worlds|
... """
>>> astropy.io.ascii.read(table, Reader=astropy.io.ascii.FixedWidth)
rec.array([(1.2, '"hello"'), (2.4, "'s worlds")],
      dtype=[('Col1', '<f8'), ('Col2', '|S9')])

Typical fixed format table with col names provided

>>> table = """
... # comment (with blank line above)
... |  Col1  |  Col2   |
... |  1.2   | "hello" |
... |  2.4   |'s worlds|
... """
>>> astropy.io.ascii.read(table, Reader=astropy.io.ascii.FixedWidth, names=('name1', 'name2'))
rec.array([(1.2, '"hello"'), (2.4, "'s worlds")],
      dtype=[('name1', '<f8'), ('name2', '|S9')])

Weird input table with data values chopped by col extent

>>> table = """
...   Col1  |  Col2 |
...   1.2       "hello"
...   2.4   sdf's worlds
... """
>>> astropy.io.ascii.read(table, Reader=astropy.io.ascii.FixedWidth)
rec.array([(1.2, '"hel'), (2.4, "df's wo")],
      dtype=[('Col1', '<f8'), ('Col2', '|S7')])

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|
... """
>>> astropy.io.ascii.read(table, Reader=astropy.io.ascii.FixedWidth)
rec.array([('John', '555-1234', '192.168.1.10'),
       ('Mary', '555-2134', '192.168.1.12'),
       ('Bob', '555-4527', '192.168.1.9')],
      dtype=[('Name', '|S4'), ('Phone', '|S8'), ('TCP', '|S12')])

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
... """
>>> astropy.io.ascii.read(table, Reader=astropy.io.ascii.FixedWidth, delimiter=' ')
rec.array([('John', '555-1234', '192.168.1.10'),
       ('Mary', '555-2134', '192.168.1.12'),
       ('Bob', '555-4527', '192.168.1.9')],
      dtype=[('Name', '|S4'), ('--Phone-', '|S8'), ('----TCP-----', '|S12')])

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|
... """
>>> astropy.io.ascii.read(table, Reader=astropy.io.ascii.FixedWidth,
...                 header_start=None, data_start=0)
rec.array([('John', '555-1234', '192.168.1.10'),
       ('Mary', '555-2134', '192.168.1.12'),
       ('Bob', '555-4527', '192.168.1.9')],
      dtype=[('col1', '|S4'), ('col2', '|S8'), ('col3', '|S12')])

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|  "]
>>> astropy.io.ascii.read(table, Reader=astropy.io.ascii.FixedWidth,
...                 header_start=None, data_start=0,
...                 names=('Name', 'Phone', 'TCP'))
rec.array([('John', '555-1234', '192.168.1.10')],
      dtype=[('Name', '|S4'), ('Phone', '|S8'), ('TCP', '|S12')])

FixedWidthNoHeader

Table with no header row and auto-column naming. Use the FixedWidthNoHeader convenience class.

>>> table = """
... |  John  | 555-1234 |192.168.1.10|
... |  Mary  | 555-2134 |192.168.1.12|
... |   Bob  | 555-4527 | 192.168.1.9|
... """
>>> astropy.io.ascii.read(table, Reader=astropy.io.ascii.FixedWidthNoHeader)
rec.array([('John', '555-1234', '192.168.1.10'),
       ('Mary', '555-2134', '192.168.1.12'),
       ('Bob', '555-4527', '192.168.1.9')],
      dtype=[('col1', '|S4'), ('col2', '|S8'), ('col3', '|S12')])

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 0 to 5 will select the first 6 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
... """
>>> astropy.io.ascii.read(table, Reader=astropy.io.ascii.FixedWidthNoHeader,
...                 names=('Name', 'Phone', 'TCP'),
...                 col_starts=(0, 9, 18),
...                 col_ends=(5, 17, 28),
...                 )
rec.array([('John', '555- 1234', '192.168.1.'),
       ('Mary', '555- 2134', '192.168.1.'),
       ('Bob', '555- 4527', '192.168.1')],
      dtype=[('Name', '|S4'), ('Phone', '|S9'), ('TCP', '|S10')])

FixedWidthTwoLine

Typical fixed format table with two header lines with some cruft

>>> table = """
...   Col1    Col2
...   ----  ---------
...    1.2xx"hello"
...   2.4   's worlds
... """
>>> astropy.io.ascii.read(table, Reader=astropy.io.ascii.FixedWidthTwoLine)
rec.array([(1.2, '"hello"'), (2.4, "'s worlds")],
      dtype=[('Col1', '<f8'), ('Col2', '|S9')])

Restructured text table

>>> table = """
... ======= ===========
...   Col1    Col2
... ======= ===========
...   1.2   "hello"
...   2.4   's worlds
... ======= ===========
... """
>>> astropy.io.ascii.read(table, Reader=astropy.io.ascii.FixedWidthTwoLine,
...                 header_start=1, position_line=2, data_end=-1)
rec.array([(1.2, '"hello"'), (2.4, "'s worlds")],
      dtype=[('Col1', '<f8'), ('Col2', '|S9')])

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

>>> table = """
... +------+----------+
... | Col1 |   Col2   |
... +------|----------+
... |  1.2 | "hello"  |
... |  2.4 | 's worlds|
... +------+----------+
... """
>>> astropy.io.ascii.read(table, Reader=astropy.io.ascii.FixedWidthTwoLine, delimiter='+',
...                 header_start=1, position_line=0, data_start=3, data_end=-1)
rec.array([(1.2, '"hello"'), (2.4, "'s worlds")],
      dtype=[('Col1', '<f8'), ('Col2', '|S9')])

Writing

FixedWidth

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 = astropy.io.ascii.read(table, Reader=astropy.io.ascii.FixedWidth)

Write a table as a normal fixed width table.

>>> astropy.io.ascii.write(dat, Writer=astropy.io.ascii.FixedWidth)
| 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.

>>> astropy.io.ascii.write(dat, Writer=astropy.io.ascii.FixedWidth, 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.

>>> astropy.io.ascii.write(dat, Writer=astropy.io.ascii.FixedWidth, 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.

>>> astropy.io.ascii.write(dat, Writer=astropy.io.ascii.FixedWidth, 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.

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

FixedWidthNoHeader

Write a table as a normal fixed width table.

>>> astropy.io.ascii.write(dat, Writer=astropy.io.ascii.FixedWidthNoHeader)
| 1.2 |   "hello" | 1 | a |
| 2.4 | 's worlds | 2 | 2 |

Write a table as a fixed width table with no padding.

>>> astropy.io.ascii.write(dat, Writer=astropy.io.ascii.FixedWidthNoHeader, 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.

>>> astropy.io.ascii.write(dat, Writer=astropy.io.ascii.FixedWidthNoHeader, bookend=False)
1.2 |   "hello" | 1 | a
2.4 | 's worlds | 2 | 2

Write a table as a fixed width table with no delimiter.

>>> astropy.io.ascii.write(dat, Writer=astropy.io.ascii.FixedWidthNoHeader, bookend=False,
...                  delimiter=None)
1.2    "hello"  1  a
2.4  's worlds  2  2

FixedWidthTwoLine

Write a table as a normal fixed width table.

>>> astropy.io.ascii.write(dat, Writer=astropy.io.ascii.FixedWidthTwoLine)
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.

>>> astropy.io.ascii.write(dat, Writer=astropy.io.ascii.FixedWidthTwoLine,
...                  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.

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