I need a Python program that will read a data file, perform an analysis, and write the results to a separate file with a .txt extension. The data is the September temperature anomalies from 1910 to 2020 in North America. I want the program to find the average temperature anomaly of each decade, find the decade with the lowest average anomaly, and the decade with the highest average anomaly. After that the program needs to write its results on a separate .txt file. Here is the data:

1910,-0.21
1911,-0.08
1912,-0.86
1913,-0.94
1914,-0.19
1915,-0.51
1916,-0.37
1917,-0.07
1918,-0.90
1919,0.21
1920,0.00
1921,0.12
1922,0.32
1923,0.08
1924,-0.63
1925,0.27
1926,-0.65
1927,-0.01
1928,-0.59
1929,-0.42
1930,0.15
1931,1.07
1932,0.17
1933,0.52
1934,-0.78
1935,-0.20
1936,0.12
1937,0.47
1938,1.35
1939,0.30
1940,1.01
1941,-0.39
1942,-0.23
1943,-0.04
1944,0.39
1945,-0.34
1946,0.10
1947,0.11
1948,0.66
1949,0.01
1950,-0.05
1951,-0.07
1952,0.32
1953,0.38
1954,0.39
1955,0.02
1956,-0.48
1957,0.30
1958,0.23
1959,-0.03
1960,0.44
1961,-0.57
1962,-0.19
1963,0.45
1964,-0.62
1965,-1.44
1966,0.47
1967,0.38
1968,0.04
1969,-0.04
1970,-0.44
1971,-0.07
1972,-1.12
1973,0.12
1974,-1.08
1975,-0.50
1976,0.24
1977,0.46
1978,0.22
1979,0.41
1980,-0.16
1981,0.22
1982,-0.10
1983,0.06
1984,-0.94
1985,-0.61
1986,-0.43
1987,0.76
1988,0.01
1989,0.16
1990,0.79
1991,0.10
1992,-1.01
1993,-0.57
1994,0.58
1995,0.56
1996,-0.16
1997,1.24
1998,1.70
1999,0.37
2000,0.20
2001,1.11
2002,1.00
2003,0.60
2004,0.24
2005,1.15
2006,0.56
2007,0.57
2008,0.35
2009,1.49
2010,0.82
2011,1.41
2012,1.40
2013,1.39
2014,0.75
2015,1.51
2016,1.39
2017,1.41
2018,0.31
2019,1.72
2020,0.73