Python：从文件列表中读取变量以计算方程式

Question

I have to calculate different equation (we assume 3 reactions). Each one uses a different variable and I have to read this variable from a file list.txt . So my idea is:

f = open('list.txt')
lines = f.readlines()

k1 = lines[0]

r1 = k1 * 2  # this is first equation 
print(r1) 

k2 = lines[1]  # second equation
r2 = k2 * 2
print(r2) 

k3 = lines[2]
r3 = k3 * 3
print (r3) 

My list is:

1
2
3

but this code prints first line two times, the second line three times and so on. Instead, I want that k1 , k2 and k3 as a variable in order to obtain in this case:

r1 = 2
r2 = 6
r3 = 9.

How can I do to obtain this result?

Answer 1

it's clear here that if you read a file with readlines(), it will return a string. So, when you want to do a math calculation, you need to convert it to integer first

f=open('list.txt')
lines=f.readlines()

k1=int(lines[0]) # convert to integer

r1=k1*2  #this is first equation 
print (r1) 

k2=int(lines[1])  #second equation
r2=k2*2
print (r2) 

k3=int(lines[2])
r3=k3*3
print (r3)

Answer 2

when you use the * operator on strings, you multiple them. for example: "a"*3 will be "aaa" and when you use it on numbers you perform the math operation. for example: 3*6=18

each line is string, so you need to cast the line to int: int(line) .

also, you should consider use the map function.

it will make your life easier.

map perform given function on every item in the list.

for example:

result = list(map(lambda x: int(x) * 3, lines))

it takes every item in the list, cast it to int, and multiply it by 3.