How do I use getattr in conjunction with dict string formatting?

I have a data structure class and a table formatting class in which I want to format a file and output it. I want the flexibility of creating formatters on the fly if the output needs to be changed.

class Row(object):
__slots__ = ('date', 'item', 'expiration', 'price')
def __init__(self, date, item, expiration, price=None):
self.date = date
self.item = item
self.expiration = expiration
self.price = ""

if price:
self.price = price

class Formatter(object):
def row(self, rowdata):
for item in rowdata:
print('<obj date="{date}" item="{item}" exp="{expiration}" price="{price}" />n').format(**item)


def print_table(objects, colnames, formatter):
for obj in objects:
rowdata = [str(getattr(obj, colname)) for colname in colnames]
formatter.row(rowdata)


I'm calling this like so:

data = [Row("20180101", "Apples", "20180201", 1.50),
Row("20180101", "Pears", "20180201", 1.25)]

formatter = Formatter()
print_table(data, ['date','item','expiration','price'], formatter)


What I'm expecting to see is:

<obj date="20180101" item="Apples" exp="20180201" price="1.50" />
<obj date="20180101" item="Pears" exp="20180201" price="1.25" />

<obj date="20180101" item="Apples" exp="20180201" price="1.50" />
<obj date="20180101" item="Pears" exp="20180201" price="1.25" />

I am currently getting the following error:
TypeError: format() argument after ** must be a mapping, not str

TypeError: format() argument after ** must be a mapping, not str

Can anyone help with this? Thanks

rowdata

2 Answers
2

Fixed code:

class Formatter(object):
def row(self, rowdata):
print('<obj date="{date}" item="{item}" exp="{expiration}" price="{price}" />n'.format(**rowdata))


def print_table(objects, colnames, formatter):
for obj in objects:
rowdata = {colname: str(getattr(obj, colname)) for colname in colnames}
formatter.row(rowdata)


You had 3 problems:

{colname: str(getattr(obj, colname)) for colname in colnames}

.format()

format()

print()

**item is invalid because the ** operator expects the named variable to be a dictionary (a mapping), and you have not provided that (item is a string). Thus, you need to convert item into a dictionary with the proper key/value pairs that you want in your format statement.

**item

**

item

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