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, 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.
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 masked=False length=2>
Col1 Col2
float64 string72
------- ---------
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 masked=False length=2>
name1 name2
float64 string72
------- ---------
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 masked=False length=2>
Col1 Col2
float64 string56
------- --------
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 masked=False length=3>
Name Phone TCP
string32 string64 string96
-------- -------- ------------
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 masked=False length=3>
Name --Phone- ----TCP-----
string32 string64 string96
-------- -------- ------------
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 masked=False length=3>
col1 col2 col3
string32 string64 string96
-------- -------- ------------
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 masked=False length=3>
Name Phone TCP
string32 string64 string96
-------- -------- ------------
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 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|
... """
>>> ascii.read(table, format='fixed_width_no_header')
<Table masked=False length=3>
col1 col2 col3
string32 string64 string96
-------- -------- ------------
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 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
... """
>>> ascii.read(table, format='fixed_width_no_header',
... names=('Name', 'Phone', 'TCP'),
... col_starts=(0, 9, 18),
... col_ends=(5, 17, 28),
... )
<Table masked=False length=3>
Name Phone TCP
string32 string72 string80
-------- --------- ----------
John 555- 1234 192.168.1.
Mary 555- 2134 192.168.1.
Bob 555- 4527 192.168.1
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 masked=False length=2>
Col1 Col2
float64 string72
------- ---------
1.2 "hello"
2.4 's worlds
Restructured text 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 masked=False length=2>
Col1 Col2
float64 string72
------- ---------
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 masked=False length=2>
Col1 Col2
float64 string72
------- ---------
1.2 "hello"
2.4 's worlds
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 |
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
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|