Double for loop to Python list comprehension

Question

I have the following (simplified structure):

class Wafer:
    def __init__(self, df):
        self.dose_fields = df

class Data:
    def __init__(self, add_zero):
        self.wafers = []
        self.wafers.append(Wafer([1.0, 1.5]))
        self.wafers.append(Wafer([2.0, 2.0]))
        self.wafers.append(Wafer([3.0, 3.5]))
        self.wafers.append(Wafer([4.0, 4.5]))

        if add_zero:
            self.wafers.append(Wafer([5.0, 0.0]))

I want to have a function that returns False when there is a zero in one of the dose_fields values.

like this:

data = Data(True)        
res = True
for wafer in data.wafers:
    for fld in wafer.dose_fields:
        if fld == 0.0:
            res = False
print res

data = Data(False)        
res = True
for wafer in data.wafers:
    for fld in wafer.dose_fields:
        if fld == 0.0:
            res = False
print res

This prints False resp. True (what I want).

However, when I try to use list comprehension:

data = Data(True)
print [df for df in wafer.dose_fields for wafer in data.wafers]
print res

data = Data(False)
print [df for df in wafer.dose_fields for wafer in data.wafers]
print res

I get the result

[4.0, 4.0, 4.0, 4.0, 4.0, 4.5, 4.5, 4.5, 4.5, 4.5]
True

resp

[5.0, 5.0, 5.0, 5.0, 5.0, 0.0, 0.0, 0.0, 0.0, 0.0]
True

Somehow I get repeats of the last item, while I want the complete list and check afterwards if there is a 0.0 inside.

What should I do to 'repair' the list comprehension statement?

The loops in LC are not in correct order.

Ashwini Chaudhary
– Ashwini Chaudhary

2015-03-02 11:30:17 +00:00
Commented Mar 2, 2015 at 11:30 — Ashwini Chaudhary
– Ashwini Chaudhary, Commented Mar 2, 2015 at 11:30

loopbackbee · Accepted Answer · 2015-03-02 11:31:55Z

2

If testing for the presence of 0.0 is really all you want, you should use the in operator. Not only is it far more readable, it's much faster. You can then use any, too

Instead of:

res = True
for wafer in data.wafers:
    for fld in wafer.dose_fields:
        if fld == 0.0:
            res = False

do

res= not any([0.0 in wafer.dose_fields for wafer in data.wafers])

answered Mar 2, 2015 at 11:31

loopbackbee

23.6k11 gold badges69 silver badges102 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Daniel Roseman · Accepted Answer · 2015-03-02 11:30:39Z

2

Nested list comprehensions can be a bit confusing. You actually need to write them in the same order as the for loops they replace: so it should be

[df for wafer in data.wafers for df in wafer.dose_fields]

answered Mar 2, 2015 at 11:30

Daniel Roseman

602k68 gold badges910 silver badges923 bronze badges

Collectives™ on Stack Overflow

Double for loop to Python list comprehension

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related