Problem Formulation

Given a CSV file (e.g., stored in the file with name 'my_file.csv').

INPUT: file 'my_file.csv'

9,8,7
6,5,4
3,2,1

Challenge: How to convert the CSV file to a list of tuples, i.e., putting the row values into the inner tuples?

OUTPUT: Python list of tuples

[(9, 8, 7), (6, 5, 4), (3, 2, 1)]

Method 1: csv.reader()

To convert a CSV file 'my_file.csv' into a list of tuples in Python, use csv.reader(file_obj) to create a CSV file reader that holds an iterable of lists, one per row. Now, use the list(tuple(line) for line in reader) expression with a generator expression to convert each inner list to a tuple.

Here’s a simple example that converts our CSV file to a nested list using this approach:

import csv csv_filename = 'my_file.csv' with open(csv_filename) as f: reader = csv.reader(f) lst = list(tuple(line) for line in reader)

Output:

print(lst)

# [('9', '8', '7'), ('6', '5', '4'), ('3', '2', '1')]

Method 2: One-Liner

You can also convert a CSV to a list of tuples using the following Python one-liner idea:

Open the file using open(), pass the file object into csv.reader(), and convert the CSV reader object to a list using the list() built-in function in Python with a generator expression to convert each inner list to a tuple.

Here’s how that looks:

import csv; lst=list(tuple(line) for line in csv.reader(open('my_file.csv'))); print(lst)

Concise, isn’t it?

The output is the same:

[('9', '8', '7'), ('6', '5', '4'), ('3', '2', '1')]

By the way: Do you need all inner elements converted to a certain data type such as integer?

If so, use the following approach on top of the previously shown list lst:

new_lst = [tuple(int(x) for x in inner) for inner in lst]

The converted new_lst now contains a list of tuples of ints:

print(new_lst)

# [('9', '8', '7'), ('6', '5', '4'), ('3', '2', '1')]

Method 3: Pandas

You can convert a CSV to a list of tuples with Pandas by first reading the CSV without header line using pd.read_csv('my_file.csv', header=None) function and second converting the resulting DataFrame to a nested list using df.values.tolist(). Third, convert the nested list to a list of tuples and you’re done.

Here’s an example that converts the CSV to a Pandas DataFrame and then to a nested raw Python list and then to a list of tuples:

import pandas as pd # CSV to DataFrame

df = pd.read_csv('my_file.csv', header=None) # DataFrame to List of Lists

lst = df.values.tolist() # List of Lists to List of Tuples:

new_lst = [tuple(x) for x in lst] print(new_lst)

# [(9, 8, 7), (6, 5, 4), (3, 2, 1)]

This was easy, wasn’t it?

Of course, you can also one-linerize it by chaining commands like so:

# One-Liner to convert CSV to list of tuples:

lst = [tuple(x) for x in pd.read_csv('my_file.csv', header=None).values.tolist()]

Method 4: Raw Python No Dependency

If you’re like me, you try to avoid using dependencies if they are not needed. Raw Python is often more efficient and simple enough anyways. Also, you don’t open yourself up to unnecessary risks and complexities.

Question: So, is there a simple way to read a CSV to a list of tuples in raw Python without external dependencies?

Sure!

To read a CSV to a list of tuples in pure Python, open the file using open('my_file.csv'), read all lines into a variable using f.readlines(). Iterate over all lines, strip them from whitespace using strip(), split them on the delimiter ',' using split(','), and pass everything in the tuple() function.

You can accomplish this in a simple list comprehension statement like so:

csv_filename = 'my_file.csv' with open(csv_filename) as f: lines = f.readlines() lst = [tuple(line.strip().split(',')) for line in lines] print(lst)

Feel free to check out my detailed video in case you need a refresher on the powerful Python concept list comprehension:

Related Tutorial: Understanding List Comprehension in Python.

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To find the number of digits in an integer you can use one of the following methods:
(1) Use Iteration
(2) Use str()+len() functions
(3) Use int(math.log10(x)) +1
(4) Use Recursion

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Problem Formulation

• Given: An integer value.
• Question: Find the number of digits in the integer/number given.

Test Cases:

Input:

num = 123

Output: 3

=========================================

Input:

num = -123

Output: 3

=========================================

Input: num = 0

Output: 1 

Method 1: Iterative Approach

Approach:

• Use the built-in abs() method to derive the absolute value of the integer. This is done to take care of negative integer values entered by the user.
• If the value entered is 0 then return 1 as the output. Otherwise, follow the next steps.
• Initialize a counter variable that will be used to count the number of digits in the integer.
• Use a while loop to iterate as long as the number is greater than 0. To control the iteration condition, ensure that the number is stripped of its last digit in each iteration. This can be done by performing a floor division (num//10) in each iteration. This will make more sense when you visualize the tabular dry run of the code given below.
• Every time the while loop satisfies the condition for iteration, increment the value of the counter variable. This ensures that the count of each digit in the integer gets taken care of with the help of the counter variable.

Code:

num = int(input("Enter an Integer: "))

num = abs(num)

digit_count = 0

if num == 0: print("Number of Digits: ", digit_count)

else: while num != 0: num //= 10 digit_count += 1 print("Number of Digits: ", digit_count)

Output:

Test Case 1:

Enter an Integer: 123

Number of Digits: 3 Test Case 2:

Enter an Integer: -123

Number of Digits: 3 Test Case 3:

Enter an Integer: 0

Number of Digits: 1

Explanation through tabular dry run:

Readers Digest:

Python’s built-in abs(x) function returns the absolute value of the argument x that can be an integer, float, or object implementing the __abs__() function. For a complex number, the function returns its magnitude. The absolute value of any numerical input argument -x or +x is the corresponding positive value +x. Read more here.

Method 2: Using str() and len()

Approach: Convert the given integer to a string using Python’s str() function. Then find the length of this string which will return the number of characters present in it. In this case, the number of characters is essentially the number of digits in the given number.

To deal with negative numbers, you can use the abs() function to derive its absolute value before converting it to a string. Another workaround is to check if the number is a negative number or not and return the length accordingly, as shown in the following code snippet.

Code:

num = int(input("Enter an Integer: "))

if num >= 0: digit_count = len(str(num))

else: digit_count = len(str(num)) - 1 # to eliminate the - sign

print("Number of Digits: ", digit_count)

Output:

Test Case 1:
Enter an Integer: 123
Number of Digits: 3

Test Case 2:
Enter an Integer: -123
Number of Digits: 3

Test Case 3:
Enter an Integer: 0
Number of Digits: 1

Alternate Formulation: Instead of using str(num), you can also use string modulo as shown below:

num = abs(int(input("Enter an Integer: ")))

digit_count = len('%s'%num)

print("Number of Digits: ", digit_count)

Method 3: Using math Module

Disclaimer: This approach works if the given number is less than 999999999999998. This happens because the float value returned has too many .9s in it which causes the result to round up.

Prerequisites: To use the following approach to solve this question, it is essential to have a firm grip on a couple of functions:

1. math.log10(x) – Simply put this function returns a float value representing the base 10 logarithm of a given number.

Example:

2. int(x) – It is a built-in function in Python that converts the passed argument x to an integer value. For example, int('24') converts the passed string value '24' into an integer number and returns 24 as the output. Note that the int() function on a float argument rounds it down to the closest integer.

Example:

Approach:

• Use the math.log(num) function to derive the base 10 logarithm value of the given integer. This value will be a floating-point number. Hence, convert this to an integer.
• As a matter of fact, when the result of the base 10 logarithm representation of a value is converted to its integer representation, then the integer value returned will almost most certainly be an integer value that is 1 less than the number of digits in the given number.
• Thus add 1 to the value returned after converting the base 10 logarithm value to an integer to yield the desired output.
• To take care of conditions where:
  
  • Given number = 0 : return 1 as the output.
  • Given number < 0 : negate the given number to ultimately convert it to its positive magnitude as: int(math.log10(-num)).

Code:

import math

num = int(input("Enter an Integer: "))

if num > 0: digit_count = int(math.log10(num))+1

elif num == 0: digit_count = 1

else: digit_count = int(math.log10(-num))+1

print("Number of Digits: ", digit_count)

Output:

Test Case 1:
Enter an Integer: 123
Number of Digits: 3

Test Case 2:
Enter an Integer: -123
Number of Digits: 3

Test Case 3:
Enter an Integer: 0
Number of Digits: 1

Method 4: Using Recursion

Recursion is a powerful coding technique that allows a function or an algorithm to call itself again and again until a base condition is satisfied. Thus, we can use this technique to solve our question.

Code:

def count_digits(n): if n < 10: return 1 return 1 + count_digits(n / 10) num = int(input("Enter an Integer: "))

num = abs(num)

print(count_digits(num))

Output:

Test Case 1:
Enter an Integer: 123
Number of Digits: 3

Test Case 2:
Enter an Integer: -123
Number of Digits: 3

Test Case 3:
Enter an Integer: 0
Number of Digits: 1

Exercise

Question: Given a string. How will you cont the number of digits, letters, spaces and other characters in the string?

Solution:

text = 'Python Version 3.0'

digits = sum(x.isdigit() for x in text)

letters = sum(x.isalpha() for x in text)

spaces = sum(x.isspace() for x in text)

others = len(text) - digits - letters - spaces

print(f'No. of Digits = {digits}')

print(f'No. of Letters = {letters}')

print(f'No. of Spaces = {spaces}')

print(f'No. of Other Characters = {others}')

Output:

No. of Digits = 2
No. of Letters = 13
No. of Spaces = 2
No. of Other Characters = 1

Explanation: Check if each character in the given string is a digit or a letter or a space or any other character or not using built-in Python functions. In each case find the cumulative count of each type with the help of the sum() method. To have a better grip on whats happening in the above code it is essential to understand the different methods that have been used to solve the question.

• isdigit(): Checks whether all characters in a given are digits, i.e., numbers from 0 to 9 (True or False).
• isalpha(): Checks whether all charactersof a given string are alphabetic (True or False).
• isspace(): Checks whether all characters are whitespaces (True or False).
• sum(): returns the sum of all items in a given iterable.

Conclusion

We have discussed as many as four different ways of finding number of digits in an integer. We also solved a similar exercise to enhance our skills. I hope you enjoyed this question and it helped to sharpen your coding skills. Please stay tuned and subscribe for more interesting coding problems.

Recommended Read: Coding Interview Questions

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