Remove last charecter from text-encoded file (UTF-8 is supported).

remove_last_char.py

#!/usr/bin/env python3
from types import SimpleNamespace as Namespace
import sys

# Future function from np_chaonay.main
def tmp(err,status_msg=None,IsWarning=False):
	name=type(err).__name__
	if not IsWarning:
		type_='Error'
		if status_msg==None: status_msg='Program operation has error due to Python exception.'
	else:
		type_='Warning'
		if status_msg==None: status_msg='Program operation has warning due to Python exception.'
	print(
		'['+type_+'] '+status_msg,
		'  From Python exception detailed information:',
		'  Exception Name: '+name,
	sep='\n')
	if len(err.args)!=0:
		print('  Exception arguments:')
		print('  [Index/Data Table]')
		print('  '+'0 (General message)'+' : '+str(err.args[0]))
		for i,j in enumerate(err.args[1:]): print('  '+str(i+1)+' : '+str(j))
	else:
		print('  Exception arguments: No any arguments.')
npc_m=Namespace()
npc_m.print_err=tmp

try: file_path=sys.argv[1]
except IndexError:
	print(sys.argv[0]+': [Error] No file path is inputted.')
	exit(2)
try:
	try: char_bin=int(sys.argv[2])
	except ValueError:
		print(sys.argv[0]+': [Error] char_bin should be integer in range [1,inf).')
		exit(2)
	if char_bin<1:
		print(sys.argv[0]+': [Error] char_bin should be integer in range [1,inf).')
		exit(2)
except IndexError: char_bin=125000
print(
	'######## Details ########','\n'
	'Selected path : ',file_path,'\n',
	'Charecter bin : ',char_bin,'\n',
	'\n','Reading...',
sep='')
with open(file_path) as file_buf:
	tmp3=0
	while True:
		tmp1=file_buf.read(char_bin)
		tmp2=len(tmp1)
		tmp3+=tmp2
		if tmp2==char_bin: continue
		else: break
	if tmp3==0:
		print('[WARNING] File has no data.')
		exit(2)
	if tmp3>=11:
		file_buf.seek(tmp3-11)
		msg=file_buf.read(11)
		msg_head=repr(msg[0])[1:-1]
		msg_middle=repr(msg[1:-1])[1:-1]
		msg_tail=repr(msg[-1])[1:-1]
		msg_old=msg_middle+msg_tail
		msg_new=msg_head+msg_middle
	else:
		file_buf.seek(0)
		msg=file_buf.read(tmp3)
		msg_old=repr(msg)[1:-1]
		msg_new=repr(msg[:-1])[1:-1]
	msg_old='Before: '+msg_old
	msg_new=' After: '+msg_new
print(
	'\n######## Change Confirmation ########','\n',
	'Last 10 characters comparison (Preview from repr of Python string):','\n',msg_old,'\n',msg_new,
sep='')
try: input('Confirm? (Enter:Proceed, Ctrl+C:QuitWithoutAnyChange)')
except (KeyboardInterrupt,EOFError): print('\nCancelled.'); exit()
print('\n######## File Operation ########')
try:
	with open(file_path,'r+') as file_buf:
		print('Truncating...')
		file_buf.seek(tmp3-1)
		file_buf.truncate()
		print('Completed.')
except Exception as err:
	print('[ERROR] Failed. However most of the situation, file isn\'t changed yet.')
	npc_m.print_err(err)
	exit(1)