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Python Itertools Tutorial – Part IV


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See Part IPart II  and in Part III this series to get familiar with itertools.

The takewhile() iterator

This iterator is the opposite of the dropwhile() iterator. In this function, it will return the outputs till the conditions return false. As you have guessed it, you can use the two iterators according to your needs. The sample code for this iterator is as follows:

# Takewhile() itertool
data = tesla[‘Close’]
result = itertools.takewhile(lambda x: x>700, data)
for each in result:

The output is given as follows:


The filterfalse() iterator

Most of the iterators are self-explanatory, and filterfalse() is no exception. This iterator will only return the element if the condition is false.

For example, if we want only those daily returns which are negative, we will put the condition that the daily returns should be more than 0 and the filterfalse() iterator will give us the required values. Let’s see how we use it in Python.

# Filterfalse() itertool
data = tesla[‘daily_returns’]
result = itertools.filterfalse(lambda x: x>0, data)
for each in result:

The output is as follows:


In the next installment, the author will discuss the islice() iterator.

Visit for ready-to-use Python functions as applied in trading and data analysis.

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