add python snippet to find srt timestamp difference

README.org

@@ -2,4 +2,9 @@
 Some scripts that I made for myself..
 
  - pdfscript.py: process pdf files
- - submixer.sh: merge ~.srt~ files into ~.ass~ files
+ - submixer.sh: merge two ~.srt~ files into a ~.ass~ file
+ - interests.py: Find simple interest and compound interest
+ - calsh.sh: An interactive interface to the ~cal~ command
+ - z-eyes.sh: take breaks to rest eys while on computer (20-20-20 rule)
+
+ - subs-helper.py: Find difference between two srt timestamps

interests.py

@@ -0,0 +1,45 @@
+"""
+Functions to find simple and compound interests.
+"""
+
+def comp_interest(principal: float,
+                  rate: float,
+                  comp_freq: int,
+                  duration: float) -> float:
+    """
+    principal: principal amount
+    rate: Rate interest as float (100% is 100)
+    duration: Duration in years
+    comp_freq: Number of compounding periods in a year
+
+    interest = principal*((1 + rate/100)**n) - principal
+    """
+    rate /= 100 * comp_freq
+    rv = (1 + rate) ** (comp_freq * duration)
+    rv = principal * rv 
+    rv -= principal
+    return rv
+
+def simp_interest(principal: float,
+                  rate: float,
+                  duration: float) -> float:
+    """
+    principal: principal amount
+    rate: Rate interest as float (100% is 100)
+    duration: Duration in years
+    comp_freq: Number of compounding periods in a year
+
+    interest = principal * duration * rate
+    """
+    return principal * duration * rate/100 
+
+
+#import pytest
+#
+#@pytest.mark.parametrize("principal,rate,comp_freq,duration,expected", [
+#    (12000, 10, 2, 1.5, 1891.5),
+#    (1000, 20, 1, 2, 440.0),
+#])
+#def test_comp_interest(principal, rate, comp_freq, duration, expected):
+#    rv = comp_interest(principal, rate, comp_freq, duration)
+#    assert round(rv, 5) == expected

subs-helper.py

@@ -0,0 +1,52 @@
+# A snippet to calculate difference between two srt timestamps
+
+def str2msecs(timestr: str) -> int:
+    """
+    Convert srt timestamp to a millisecond int value
+
+    >>> str2msecs("00:00:00,052")
+    52
+    """
+    hrs_str, mins_str, rem = timestr.split(":")
+    secs_str, msecs_str = rem.split(",")
+    hrs, mins = int(hrs_str), int(mins_str)
+    secs, msecs = int(secs_str), int(msecs_str)
+    rv = hrs*3600 + mins*60 + secs
+    return rv*1000 + msecs
+    
+def msecs2str(msecs: float) -> str:
+    """
+    Convert a millisecond int value to srt timestamp
+
+    >>> msecs2str(52)
+    '00:00:00,052'
+    >>> msecs2str(52.488)
+    '00:00:00,052'
+    """
+    hrs, rem = divmod(msecs, 3600000)
+    mins, rem = divmod(rem, 60000)
+    secs, msecs = divmod(rem, 1000)
+    hrs, mins, secs, msecs = int(hrs), int(mins), int(secs), int(msecs)
+
+    # https://docs.python.org/3/library/string.html#format-specification-mini-language
+    return f"{hrs:02d}:{mins:02d}:{secs:02d},{msecs:03d}"
+
+def foo(s1: str, s2: str) -> float:
+    """
+    Take 2 timestamps and find difference between them
+    ie,
+    foo(s1, s2) = s1 - s2
+
+    >>> foo("00:00:59,128", "00:00:06,640")
+    52.488
+    """
+    a = str2msecs(s1)
+    b = str2msecs(s2)
+    #return msecs2str(a-b)
+    return (a-b) / 1000
+
+a = foo("00:00:59,128", "00:00:06,640")
+# 52.488
+
+print(a)
+print(msecs2str(a))