Cell Patterns

Cell patterns allow you to normalize the data on a per-field basis.

fuzzytable Built-Ins

Let’s say you have this very simple table:

Name	DOB
John Doe	1995
123	2003OCt
Jane Doe	1964
True	2019

You want to ensure the first field (Name) returns only strings and the Birthday column returns integers.

# birthdays.py

from fuzzytable import FuzzyTable, FieldPattern, cellpatterns

name_field = FieldPattern(
    name="name",
    alias="Name",
    cellpattern=cellpatterns.String,
)

birthday_field = FieldPattern(
    name="birthday",
    alias="DOB",
    cellpattern=cellpatterns.Integer,
)

birthday_table = FuzzyTable(
    path='birthdays.csv',
    fields=[name_field, birthday_field],
)

>>> python birthdays.py
>>> for record in birthday_table.records
...     print(record)
...
{'name': 'John Doe', 'birthday': 1995}
{'name': '123', 'birthday': 2003}
{'name': 'Jane Doe', 'birthday': 1964}
{'name': '', 'birthday': 2019}

Custom Callables

You’re not limited to the built-in cell patterns provided by fuzzytable. You can also create your own.

In this example, we’ll return the type of the variable in the Name column.

# birthdays_customcallable.py

from fuzzytable import FuzzyTable, FieldPattern, cellpatterns

# This is new
def value_type(value):
    return type(value)

name_field = FieldPattern(
    name="name",
    alias="Name",
    cellpattern=value_type,  # This is new.
    # Note that we don't call the function here.
)

birthday_field = FieldPattern(
    name="birthday",
    alias="DOB",
    cellpattern=cellpatterns.Integer,
)

birthday_table = FuzzyTable(
    path='birthdays.csv',
    fields=[name_field, birthday_field],
)

>>> python birthdays_customcallable.py
>>> for record in birthday_table.records
...     print(record)
...
{'name': <class 'str'>, 'birthday': 1995}
{'name': <class 'int'>, 'birthday': 2003}
{'name': <class 'str'>, 'birthday': 1964}
{'name': <class 'bool'>, 'birthday': 2019}

Piping

You can also string multiple cell patterns together. Here we’ll pipe the String output into a custom first_char function.

# birthdays_piping.py

from fuzzytable import FuzzyTable, FieldPattern, cellpatterns

# This is new
def first_char(value):
    # Because we are piping the output of cellpattern.String
    # to this function, value is guaranteed to be a string.
    # Therefore, the only potential exception we have to
    # handle is IndexError (in case value = '').
    try:
        return value[0]
    except IndexError:
        return ''

name_field = FieldPattern(
    name="name",
    alias="Name",
    cellpattern=[cellpatterns.String, first_char],  # This is new
)

# replace `birthday_field` with a string literal 'DOB' below.

birthday_table = FuzzyTable(
    path='birthdays.csv',
    fields=[name_field, 'DOB'],
)

>>> python birthdays_piping.py
>>> for record in birthday_table.records
...     print(record['name'])
...
'J'
'1'
'J'
''