Slicing Python strings

Question

I'm currently trying to slice a specific string into parts but alway getting out of index errors.

The string is:

columnData = "001.001.000.100.000.000.000"

myClassInstance = MyClass(
    param1 = columnData[0:3],  
    param2  = columnData[4:3], 
    param3 = columnData[8:3],  
    param4  = 0,             
    param5 = columnData[12:3], 
    param6 = columnData[16:3], 
    param7 = columnData[20:3], 
    param8 = columnData[24:3]

)

Whenever it tries to set param8 I get the out of index error.

I then tried to put the slices into a file to see where the error is and tried:

                        f = open("TestmyTset.txt","w")
                        f.write(columnData)
                        f.write("\nparam1: ")
                        f.write(columnData[0:3])
                        f.write("\nparam2r: ")
                        f.write(columnData[4:3])
                        f.close();

but param2 was never printed into the file.

The output is:

001.001.000.100.000.000.000
param1: 001
param2:

So my question here is where my error is as I tried again and again and not finding it (in effect each of the slices shall be one of the . separated parts of the string).

As asked the expected outputs would be:

param1 = "001"
param2 = "001"  (the 2nd 001 in the original string)
param3 = "000"
param4 = "0"
param5 = "100"
....

I updated the answer there so that it is clear what I would expect inside each param from the appropriate slices — Thomas
– Thomas, Commented Nov 22, 2014 at 10:21
In param4 you are expecting "100" but you have declared it as 0. — Tanveer Alam
– Tanveer Alam, Commented Nov 22, 2014 at 10:24
ok got it from the answers.....ouch confused languages again (thought length of slice instead of stop location) — Thomas
– Thomas, Commented Nov 22, 2014 at 10:28

Community · Accepted Answer · 2020-06-20 09:12:55Z

3

i think what you are trying to do is:

columnData[4:7] columnData[8:11] etc.

I think it's better to just to

split_column_data = columnData.split('.')

which splits the string at each . in the string. and returns a list

>>>print split_column_data

['001', '001', '000', ... ]

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Nov 22, 2014 at 10:23

chunpoon

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Community · Accepted Answer · 2020-06-20 09:12:55Z

2

The documentation for slice() states:

slice([start], stop[, step])

Return a slice object representing the set of indices specified by range(start, stop, step). The start and step arguments default to None. Slice objects have read-only data attributes start, stop and step which merely return the argument values (or their default). They have no other explicit functionality; however they are used by Numerical Python and other third party extensions. Slice objects are also generated when extended indexing syntax is used. For example: a[start:stop:step] or a[start:stop, i].

In other words, what you want is:

param2 = columnData[4:7]
param3 = columnData[8:11]
...

edited Jun 20, 2020 at 9:12

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answered Nov 22, 2014 at 10:23

Phylogenesis

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kedarkhetia · Accepted Answer · 2014-11-22 10:45:48Z

1

as far as I have understood your question, it seems that you want to slice a string such that

columnData = "001.001.000.100.000.000.000"

myClassInstance = MyClass(
    param1 = columnData[0:3],  
    param2  = columnData[4:3], 
    param3 = columnData[8:3],  
    param4  = 0,             
    param5 = columnData[12:3], 
    param6 = columnData[16:3], 
    param7 = columnData[20:3], 
    param8 = columnData[24:3]  
)

must set

param1 : 001
param2 : 001
param3 : 000
param4 : 0
param5 : 100
param6 : 000
param7 : 000
param8 : 000

now as far as I know

a = "123456789" to 123
print a[0:3]
print a[3:6]
.....

will give

123
456
....

so for your example you need to set

columnData = "001.001.000.100.000.000.000"

myClassInstance = MyClass(
    param1 = columnData[0:3],  
    param2  = columnData[4:7], 
    param3 = columnData[8:11],  
    param4  = 0,             
    param5 = columnData[12:15], 
    param6 = columnData[16:19], 
    param7 = columnData[20:23], 
    param8 = columnData[24:27]  
)

It will work :) good luck !

answered Nov 22, 2014 at 10:45

kedarkhetia

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Thomas Over a year ago

Accepted as it was the most complete answer (also yepp works tnx)

immortal · Accepted Answer · 2014-11-22 10:25:51Z

1

Slicing in python goes as: [start_index : end_index : step_size] - in other words what you're trying to do when you access columnData[4:3] is read from index 4 to index 3 - which is meaningless.

What you need to read is columnData[4:7] to get the result you desire.

I would also recommend you look at str.split, since columnData.split('.') will give you what you want in a far easier way.

answered Nov 22, 2014 at 10:25

immortal

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Tanveer Alam · Accepted Answer · 2014-11-22 10:32:16Z

1

columnData = "001.001.000.100.000.000.000"
param1,param2,param3,param5,param6,param7,param8 = columnData.split('.')
param4 = 0
print ("param1 :{} , param2 :{}, param3 :{}, param4: {}, param5 :{}, param6 :{}, param7 :{},param8 :{}").\
            format(param1, param2, param3, param4, param5, param6, param7, param8)


Output:
param1 :001 , param2 :001, param3 :000, param4: 0, param5 :100, param6 :000, param7 :000,param8 :000

answered Nov 22, 2014 at 10:32

Tanveer Alam

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