I have a list
task_list = ['A1.wakeup', 'A2.brush','B1.route','B2.breakfast']
the result i want is
task_list = ['1A1.wakeup', '1A2.brush','2B1.route','2B2.breakfast']
I use a for loop:
new_task_list = task_list[:]
for task in new_task_list:
task.replace('A', '1A')
task.replace('B','1B')
In [61]: new_task_list
Out[61]: ['A1.wakeup', 'A2.brush', 'B1.route', 'B2.breakfast']
It does not change, What's the problem?
str.replace does not work in-place (pun unintended).
You can create a mapping of the replacements and use a list comprehension to build the new list looking up values from the mapping an prepending those to each string:
mapping = {'A': '1', 'B': '2'}
new_list = [mapping[x[0]]+x for x in task_list]
print(new_list)
# ['1A1.wakeup', '1A2.brush', '2B1.route', '2B2.breakfast']
Taking cue from Moses Koledoye's answer
task_list = ['A1.wakeup', 'A2.brush','B1.route','B2.breakfast']
Getting the difference of ascii value of A (=65), B (=66) and 64
[ str( ord(x[0]) - 64 )+x for x in task_list ]
# ['1A1.wakeup', '1A2.brush', '2B1.route', '2B2.breakfast']
The problem is that strings in python are inmutable (they can not change), that's why replace will return a new string (the original one will be the same). To do what you want you could try:
new_task_list = task_list[:]
for idx, task in enumerate(new_task_list):
new_task_list[idx] = new_task_list[idx].replace('A', '1A')
new_task_list[idx] = new_task_list[idx].replace('B', '2B')
or even:
from operator import methodcaller
new_task_list = map(methodcaller('replace', 'B', '2B'),
map(methodcaller('replace', 'A', '1A'), task_list))
task_list = ['A1.wakeup', 'A2.brush','B1.route','B2.breakfast']
task_list = [w.replace('A', '1A') for w in task_list]
task_list = [w.replace('B', '2B') for w in task_list]
Then, you will get
task_list = ['1A1.wakeup', '1A2.brush', '2B1.route', '2B2.breakfast']
task in your for loop is just a variable updated on each loop iteration, task.replace('A', '1A') doesn't change the list value inplace.
I would suggest the following solution with re module:
import re
task_list = ['A1.wakeup', 'A2.brush','B1.route','B2.breakfast']
new_task_list = [ re.sub(r'^(A|B)', lambda m: ('1' if m.group(1) == 'A' else '2') + m.group(1), t)
for t in task_list]
print(new_task_list)
The output:
['1A1.wakeup', '1A2.brush', '2B1.route', '2B2.breakfast']
Or even simpler:
task_list = ['A1.wakeup', 'A2.brush','B1.route','B2.breakfast']
search = {'A':'1', 'B':'2'}
new_task_list = [ (search[t[0]] if t[0] in search else '') + t for t in task_list]
print(new_task_list)
