Interconversion between data types is facilitated by python libraries quite easily. But the problem of converting the entire list of strings to integers is quite common in the development domain. Let’s discuss a few ways to solve this particular problem.
Method 1: Using eval[]
Python eval[] function parse the expression argument and evaluate it as a python expression and runs Python expression[code], If the expression is an int representation, Python converts the argument to an integer.
Python3
lis = ['1', '-4', '3', '-6', '7']
res = [eval[i] for i in lis]
print["Modified list is: ", res]
Output:
Modified list is: [1, -4, 3, -6, 7]
Method 2: Naive Method
This is the most generic method that strikes any programmer while performing this kind of operation. Just looping over the whole list and converting each string of the list to int by type casting.
Python3
test_list = ['1', '4', '3', '6', '7']
for i in range[0, len[test_list]]:
test_list[i] = int[test_list[i]]
print["Modified list is : "
+ str[test_list]]
Output:
Modified list is: [1, 4, 3, 6, 7]
Method 3: Using list comprehension
This is just a kind of replica of the above method, just implemented using list comprehension, a kind of shorthand that a developer looks for always. It saves the time and complexity of coding a solution.
Python3
test_list = ['1', '4', '3', '6', '7']
test_list = [int[i] for i in test_list]
print ["Modified list is : " + str[test_list]]
Output:
Modified list is : [1, 4, 3, 6, 7]
Method 4: Using map[]
This is the most elegant, pythonic, and recommended method to perform this particular task. This function is exclusively made for this kind of task and should be used to perform them.
Python3
test_list = ['1', '4', '3', '6', '7']
test_list = list[map[int, test_list]]
print["Modified list is : " + str[test_list]]
Output:
Modified list is : [1, 4, 3, 6, 7]
Method 5: List of strings with mixed integer representations
Here, we will first convert each string to a float first and then we will convert it into an integer by using the round[] function, otherwise, it will through error.
Python3
lis = ['1.1', '4', '3.5', '6.7', '7.2']
res = [round[float[i]] for i in
lis]
print["Modified list is: ", res]
Output:
Modified list is: [1, 4, 4, 7, 7]
Given a list of integers, write a Python program to convert the given list into a single integer.
Examples:
Input : [1, 2, 3] Output : 123 Input : [55, 32, 890] Output : 5532890
There are multiple approaches possible to convert the given list into a single integer. Let’s see each one by one.
Approach #1 : Naive Method
Simply iterate each element in the list and print them without space in between.
lst =
[12, 15, 17]
for i in lst:
print[i, end=""]
Output:
121517
Approach #2 : Using join[]
Use the join[] method of Python. First convert the list of integer into a list of strings[ as join[]
works with strings only]. Then, simply join them using join[] method. It takes a time complexity of O[n].
def convert[list]:
s = [str[i] for i in list]
res = int["".join[s]]
return[res]
list = [1, 2, 3]
print[convert[list]]
Output:
123
Approach #3 : Using map[]
Another approach to convert a list of multiple integers into a single integer is to use map[] function of Python with str function to convert the Integer list to string list. After this, join them on the empty string and then cast back to integer.
def convert[list]:
res = int["".join[map[str, list]]]
return res
list = [1, 2, 3]
print[convert[list]]
Output:
123
Approach #4 : Multiplying by corresponding power of 10
A more mathematical way, which does not require to convert the integer list to string list is, to multiply each
integer element with its corresponding power of 10, and then summing it up. It takes a time complexity of O[n].
def convert[list]:
res = sum[d * 10**i for i, d in enumerate[list[::-1]]]
return[res]
list = [1, 2, 3]
print[convert[list]]
Output:
123
A small variation to this program leads to less computation in calculation of sum, i.e. using reduce[]. This makes use of Horner’s rule, which factors the polynomial representing the number to reduce the number of multiplications.
res = functools.reduce[lambda total, d: 10 *
total + d, list, 0]