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from __future__ import absolute_import, print_function, division
from petl.util.base import values, header, Table
def typeset(table, field):
"""
Return a set containing all Python types found for values in the given
field. E.g.::
>>> import petl as etl
>>> table = [['foo', 'bar', 'baz'],
... ['A', 1, '2'],
... ['B', u'2', '3.4'],
... [u'B', u'3', '7.8', True],
... ['D', u'xyz', 9.0],
... ['E', 42]]
>>> sorted(etl.typeset(table, 'foo'))
['str']
>>> sorted(etl.typeset(table, 'bar'))
['int', 'str']
>>> sorted(etl.typeset(table, 'baz'))
['NoneType', 'float', 'str']
The `field` argument can be a field name or index (starting from zero).
"""
s = set()
for v in values(table, field):
try:
s.add(type(v).__name__)
except IndexError:
pass # ignore short rows
return s
Table.typeset = typeset
def diffheaders(t1, t2):
"""
Return the difference between the headers of the two tables as a pair of
sets. E.g.::
>>> import petl as etl
>>> table1 = [['foo', 'bar', 'baz'],
... ['a', 1, .3]]
>>> table2 = [['baz', 'bar', 'quux'],
... ['a', 1, .3]]
>>> add, sub = etl.diffheaders(table1, table2)
>>> add
{'quux'}
>>> sub
{'foo'}
"""
t1h = set(header(t1))
t2h = set(header(t2))
return t2h - t1h, t1h - t2h
Table.diffheaders = diffheaders
def diffvalues(t1, t2, f):
"""
Return the difference between the values under the given field in the two
tables, e.g.::
>>> import petl as etl
>>> table1 = [['foo', 'bar'],
... ['a', 1],
... ['b', 3]]
>>> table2 = [['bar', 'foo'],
... [1, 'a'],
... [3, 'c']]
>>> add, sub = etl.diffvalues(table1, table2, 'foo')
>>> add
{'c'}
>>> sub
{'b'}
"""
t1v = set(values(t1, f))
t2v = set(values(t2, f))
return t2v - t1v, t1v - t2v
Table.diffvalues = diffvalues
def strjoin(s):
"""
Return a function to join sequences using `s` as the separator. Intended
for use with :func:`petl.transform.conversions.convert`.
"""
return lambda l: s.join(map(str, l))
def nthword(n, sep=None):
"""
Construct a function to return the nth word in a string. E.g.::
>>> import petl as etl
>>> s = 'foo bar'
>>> f = etl.nthword(0)
>>> f(s)
'foo'
>>> g = etl.nthword(1)
>>> g(s)
'bar'
Intended for use with :func:`petl.transform.conversions.convert`.
"""
return lambda s: s.split(sep)[n]
def coalesce(*fields, **kwargs):
"""
Return a function which accepts a row and returns the first non-missing
value from the specified fields. Intended for use with
:func:`petl.transform.basics.addfield`.
"""
missing = kwargs.get('missing', None)
default = kwargs.get('default', None)
def _coalesce(row):
for f in fields:
v = row[f]
if v is not missing:
return v
return default
return _coalesce
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