# Python: printing every other input using a for loop

• Comp Sci
Homework Statement:
I have to print every other input.
Relevant Equations:
you are not given input to put in or the total number of input, but the input shows a total number of strings in the first line and the rest consists of alternation of string and integer.
for example, the input can be:

3
12
tiger
11
cats
10
dogs
I want my output to read only the integers. Here's my attempt:

number = int(input())

for i in range(2, number+1, 2):
print(input())

## Answers and Replies

jedishrfu
Mentor
Here's some code that illustrates what you are trying to do. Basically if the int(some_string) fails to extract a number an exception is thrown.

https://pynative.com/python-check-user-input-is-number-or-string/
Alternatively, you could parse the string into characters and use the isdigit() function to see if all are digits or '.' or - or + ... depending on what you define as an acceptable number.

Mark44
Mentor
Homework Statement: I have to print every other input.
Homework Equations: you are not given input to put in or the total number of input, but the input shows a total number of strings in the first line and the rest consists of alternation of string and integer.
for example, the input can be:

3
12
tiger
11
cats
10
dogs

I want my output to read only the integers. Here's my attempt:

number = int(input())

for i in range(2, number+1, 2):
print(input())
The first number indicates the number of strings in the sequence of inputs. It should be used to control a for loop that runs that many times, with pairs of input calls. For example, in your sample inputs, the first number entered indicates that three strings will be in the input sequence. Because the rest of the input values alternate between integers and strings, the loop body should do two inputs: the first to input a number and the second to input a string but not do anything with it.

Notice that the problem statement says "the rest consists of alternation of string and integer." but the sample input sequence has this alternation in the opposite order. That is, as integer, string, integer, string, and so on.

I wrote a short program that appears to satisfy the program requirements, using exactly the sample inputs you wrote. Here is the output from that program.
Code:
Number of strings: 3
12
Val:  12
tiger
11
Val:  11
cats
10
Val:  10
dogs
The only output from my program are the initial prompt to enter the first number and the lines that start with Val: ...
All other lines are what I typed as inputs to the program.