wondering about format index

Question

first of all, I'm korean and i'm not good at english but i'll try my best I was wondering about format(last line of this code). this is code that making question (I used translator at #things) this is about calculating average of passerby by time zone (translator got wrong. not row. it's passerby)

import csv

a = [[],[],[],[],[],[],[]]                     # List Declaration of Size 7 x 24

# a[i] = dictionary {num, wnum, ynum} : Data to be stored in each time zone for each day of the week
# Read data from csv file and store it in a two-dimensional array a[][]
with open('passby_data.csv', 'r') as f :
    reader = csv.DictReader(f)
    i =j=  0
    for row in reader :        
        a[i].append(row)
        j = j + 1
        if(j % 24 == 0) :                       # If you read 24 data, move on to the next day of the week
            i = i + 1

# -------------------------------------------------------------------------

day_title = ['MON', 'TUE', 'WED', 'THR', 'FRI', 'SAT', 'SUN']     # the title of the day
hour_title = ['01', '02', '03', '04', '05', '06', \
              '07', '08','09', '10', '11', '12', \
              '13', '14','15', '16', '17', '18', \
              '19', '20','21', '22', '23', '24',]


# Obtain weekly averages by time zone
avgh = []
for j in range(0, 24) :                          # Repeat 19 to 24 lines for 0 to 23 hours                   
    day_sum = 0                                  # Initialize to 0 to get the sum by time zone
    # Jth Time Zone Weekly Sum
    for i in range (0, 7) :                      # Repeat seven times a week
        day_sum = day_sum + int(a[i][j]['num'])  # Accumulate the number of rows by time zone j on the i-th day of the week

    avgh.append(day_sum/7)                       # Find the average number of weekly rowers in the j-th time zone



# To output the average floating population by time zone
for j in range (0, 24) :                         # repeat 24 times
    print("[~{0}:00]: {1:4}". format(hour_title[j], int(avgh[j])))    # Output of floating population by time zone 

and this is what i got.

[~01:00]:    1
[~02:00]:    0
[~03:00]:    0
[~04:00]:    0
[~05:00]:    0
[~06:00]:    2
[~07:00]:    2
[~08:00]:   12
[~09:00]:   16
[~10:00]:   10
[~11:00]:    3
[~12:00]:   19
[~13:00]:   17
[~14:00]:    7
[~15:00]:    9
[~16:00]:   12
[~17:00]:    9
[~18:00]:    8
[~19:00]:   17
[~20:00]:   15
[~21:00]:   11
[~22:00]:    5
[~23:00]:    6
[~24:00]:    4

Process finished with exit code 0

this is what they tried. i got question at here. print("[~{0}:00]: {1:4}". format(hour_title[j], int(avgh[j]))) # Output of floating population by time zone why they're using {1:4}? not {0:4}. so i tried {0:4}.

import csv

a = [[],[],[],[],[],[],[]]                     # List Declaration of Size 7 x 24

# a[i] = dictionary {num, wnum, ynum} : Data to be stored in each time zone for each day of the week
# Read data from csv file and store it in a two-dimensional array a[][]
with open('passby_data.csv', 'r') as f :
    reader = csv.DictReader(f)
    i =j=  0
    for row in reader :        
        a[i].append(row)
        j = j + 1
        if(j % 24 == 0) :                       # If you read 24 data, move on to the next day of the week
            i = i + 1

# -------------------------------------------------------------------------

day_title = ['MON', 'TUE', 'WED', 'THR', 'FRI', 'SAT', 'SUN']     # the title of the day
hour_title = ['01', '02', '03', '04', '05', '06', \
              '07', '08','09', '10', '11', '12', \
              '13', '14','15', '16', '17', '18', \
              '19', '20','21', '22', '23', '24',]


# Obtain weekly averages by time zone
avgh = []
for j in range(0, 24) :                          # Repeat 19 to 24 lines for 0 to 23 hours                   
    day_sum = 0                                  # Initialize to 0 to get the sum by time zone
    # Jth Time Zone Weekly Sum
    for i in range (0, 7) :                      # Repeat seven times a week
        day_sum = day_sum + int(a[i][j]['num'])  # Accumulate the number of rows by time zone j on the i-th day of the week

    avgh.append(day_sum/7)                       # Find the average number of weekly rowers in the j-th time zone



# To output the average floating population by time zone
for j in range (0, 24) :                         # repeat 24 times
    print("[~{0}:00]: {0:4}". format(hour_title[j], int(avgh[j])))    # Output of floating population by time zone

and this is what i got this time.

[~01:00]: 01  
[~02:00]: 02  
[~03:00]: 03  
[~04:00]: 04  
[~05:00]: 05  
[~06:00]: 06  
[~07:00]: 07  
[~08:00]: 08  
[~09:00]: 09  
[~10:00]: 10  
[~11:00]: 11  
[~12:00]: 12  
[~13:00]: 13  
[~14:00]: 14  
[~15:00]: 15  
[~16:00]: 16  
[~17:00]: 17  
[~18:00]: 18  
[~19:00]: 19  
[~20:00]: 20  
[~21:00]: 21  
[~22:00]: 22  
[~23:00]: 23  
[~24:00]: 24  

Process finished with exit code 0

why they're using {1:4}? not {0:4}. python starts with 0. not 1. and even more, those answer are different({0:4} and {1:4}) why they are different? and why {0:4} is even shorter than {1:4}? it's not look like there are four spaces in {0:4} answer.) thanks for watching this long long explanation haha.. i hope you understand what i wanted to say,,, Have a nice day and I really appreciate for your answering.