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Python | Preceding element tuples in list

  • Last Updated : 05 Sep, 2019

Sometimes, while working with Python list, we can have a problem in which we need to construct tuples, with the preceding element, whenever that element matches a particular condition. This can have potential application in day-day programming. Let’s discuss a way in which this task can be performed.

Method : Using zip() + list comprehension
This task can be performed using the combination of above functionalities. In this, the zip() performs the task of construction of tuples and the catering of condition matching and iteration is handled by list comprehension.

Code :




# Python3 code to demonstrate working of
# Preceding Tuple elements in list
# using zip() + list comprehension
  
# initialize list
test_list = [1, 4, 'gfg', 7, 8, 'gfg', 9, 'gfg']
  
# printing original list
print("The original list is : " + str(test_list))
  
# initialize ele 
ele = 'gfg'
  
# Preceding Tuple elements in list
# using zip() + list comprehension
res = [(x, y) for x, y in zip(test_list, test_list[1 : ]) if y == ele]
  
# printing result
print("Tuple list with desired Preceding elements " + str(res))
Output :
The original list is : [1, 4, 'gfg', 7, 8, 'gfg', 9, 'gfg']
Tuple list with desired Preceding elements [(4, 'gfg'), (8, 'gfg'), (9, 'gfg')]
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