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# Calculating formulae in Excel with Python

Posted by: admin May 14, 2020 Leave a comment

Questions:

I would like to insert a calculation in Excel using Python.
Generally it can be done by inserting a formula string into the relevant cell.
However, if i need to calculate a formula multiple times for the whole column
the formula must be updated for each individual cell. For example, if i need to
calculate the sum of two cells, then for cell C(k) the computation would be A(k)+B(k).
In excel it is possible to calculate C1=A1+B1 and then automatically expand the
calculation by dragging the mouse from C1 downwards.
My question is: Is it possible to the same thing with Python, i.e. to define a formula in only one cell and then to use Excel capabilities to extend the calculation for the whole column/row?

Thank you in advance,
Sasha

How to&Answers:

As Roberto mentions, you can use xlwt and a trusty for-loop:

``````import xlwt

w = xlwt.Workbook()
ws = w.add_sheet('mysheet')

for i in range(10):
ws.write(i, 0, i)
ws.write(i, 1, i+1)
ws.write(i, 2, xlwt.Formula("\$A\$%d+\$B\$%d" % (i+1, i+1)))

w.save('myworkbook.xls')
``````

### Answer：

If you are using COM bindings, then you can simply record a macro in Excel, then translate it into Python code.
If you are using xlwt, you have to resort to normal loops in python..

### Answer：

Sasha,

Python code translated from your macro would look like this:

``````startCell = mySheet.Range("M6")
wholeRange = mySheet.Range("M6:M592")
startCell.FormulaR1C1 = "=R[-1]C[-7]/RC[-10]*R[-1]C"
startCell.AutoFill(Destination=wholeRange)
``````

Haven’t tested it, but I write this often at work. Let me know if it doesn’t work.

### Answer：

If you want to iterate in the horizontal direction, here is a function I use. 0 -> a, 26 -> aa, 723 -> aav

``````def _num_to_let(num):
if num > 25:
return _num_to_let(num/26-1) + chr(97+ num % 26)
return chr(97+num)
``````

### Answer：

If you want to iterate in xlwt for columns (in formulas) you can use Utils module from xlwt like this:

``````from xlwt import Utils
print Utils.rowcol_pair_to_cellrange(2,2,12,2)
print Utils.rowcol_to_cell(13,2)
>>>
C3:C13
C14
``````

### Answer：

Using one of the COM wrapping libraries will allow you to use a User Defined Functions written in Python. This is the domain of xlwings and PyXll.

FlyingKoala also does this as it’s an extension of xlwings. FlyingKoala has added ability to (on-the-fly) read Excel functions and convert them into Python code and evaluate the equation in Python.