Approximate compare of DateOffset strings in pandas

compare_offsets.py

# Comparing pandas DateOffset strings directly one another is not available 
# as a method of the DateOffset class in python. The reason is straightforward:
# offsets are "timestamp context" dependent. 

# For example 1M can be either 28D, 29D, 30D, or 31D so there is no way to compare
# *exactly * DateOffset strings with each other out of context. 

# To alleviate this, here below you can find a reference implementation 
# for an approximate comparison assuming months of 30 days, and years of 365 days.

def alias_to_days(x):
    return {
        "B":     1,
        "D":     1,
        "W":     7,
        "M":    30,
        "SM":   15,
        "BM":   30,
        "MS":   30,
        "SMS":  15,
        "BMS":  30,
        "Q":    90,
        "BQ":   90,
        "QS":   90,
        "BQS":  90,
        "A":   365,
        "Y":   365,
        "BA":  365,
        "BY":  365,
        "AS":  365,
        "YS":  365,
        "BAS": 365,
        "BYS": 365,
    }.get(x, None)

def alias_to_seconds(x):
    return {
        "BH":  3600,
        "H":   3600,
        "T":     60,
        "min":   60,
        "S":      1,
    }.get(x)

def alias_to_int(x):
    n= to_days(x)
    if n is not None:
        return n * 86400
    
    n= to_seconds(x)
    if n is not None:
        return n
    
    raise ValueError(f'{x} is not a valid/supported string offset')


import re
def offset_to_int(x):
    i = 0
    
    first=r"^(\d*)([a-zA-Z]+)(-[a-zA-Z]+)?(.*)$"
    
    g = re.match(first,x).groups()
    i += (int(g[0]) or 1)* alias_to_int(g[1])
    
    # handle concatenated datetime offset strings
    if g[3]:
        block=r"(\d+)([a-zA-Z]+)(-[a-zA-Z]+)?"
        for e in re.findall(block,g[3]):
            i += (int(e[0]) or 1)* alias_to_int(e[1])
    return i

def compare_offsets(a, b):
    if a==b:
        return 0
    
    a = offset_to_int(a)
    b = offset_to_int(b)
    
    if a==b:
        return 0
    elif  a>b:
        return 1
    else:
        return -1

examples.txt

>> compare_offsets('72H30T', '3D')
1

>> compare_offsets('72H', '3D')
0

>> compare_offsets('2B12BH', '3D')
-1

offset_to_int('2QS-JUN12W30T-MON69S1BH')
22815069