Reading in multiple files in Python and renaming them using string - str(i+1) not working?

You can use glob to open all files with a specified pattern. Although it's patterns follow Unix guidelines and may need to be further filtered to meet your specifications:

import glob

files = glob.glob("C_[1-2][1-9].txt")

Or just load all the correct files into a dict as it's the recommended way of creating a variable amount of variables.

files = {f"C{i}": np.loadtxt(f"{cfile}{i}.txt", delimiter=',') for i in range(16,26)}

cfile='C_'
C='What_'
H={}
for i in range(15,25):
    infile = cfile + str(i+1) + '.txt'
    #print("infile:",infile)
    k=C+str(i+1)
    H[k] = np.loadtxt(infile, delimiter=',')
    print(f"Your loaded file is here: H[{k}]")

    #PRINT OUT THE CONTENT OF THE FILE 
    print(H[k])
    
 

just use print(H[k]) to print out the content of each file. Or print( H["What_24"] ), or if you change the string of variable C = 'C_' then you can print(H["C_24"] ) and view the content of file stored inside the dict.

Why what you wanted to do was an error:

C + str(i+1) = np.loadtxt(infile, delimiter=',')

Because C is undefined ... and if it were defined like C='What_you_want' you would have gotten:

'What_you_want'+str(i+1)  ->   'What_you_want'+'number' -> 'What_you_wantnumber' 

So

'What_you_wantnumber' is a string which resides inside the variable C

np.loadtxt(infile, delimiter=',') is a method that return the content o the file as a string .

so you can't assign string = string . But you can do

variable = string

for example: the variable name = "flagello" ok

 print(name)  

output : flagello #that is as string

"flagello"="flagello"
  File "<stdin>", line 1
SyntaxError: can't assign to literal

"flagello"="silicio"
  File "<stdin>", line 1
SyntaxError: can't assign to literal

'flagello' == 'silico'  

Output: False

'flagello' == 'flagello'

Output: True

You can compare strings  but you can t assing a string to a string .

You can assign a string value  to a variable. 

But at this moment nothing rename nothing . Now you get the content of the files , assign the content of each file inside a dict ad print the content of the dict

How to rename a file

import os
os.rename(r'C_21.txt',r'CCCP_21.txt')

In this case you don't need to read the content of the file to rename it.

Just use the old name and the new name