Calculate GPA using Python

import pandas as pd
excel_path = 'GPA.xlsx'
d = pd.read_excel(excel_path, sheetname=None)

D:\anacorda\lib\site-packages\pandas\io\excel.py:329: FutureWarning: The `sheetname` keyword is deprecated, use `sheet_name` instead
  **kwds)

df = pd.DataFrame(d['Sheet1'],columns=['學年度學期','選別', '科目名稱', '學分','成績','GPA 4.3','GPA 4.0'])
df.head(5)

	學年度學期	選別	科目名稱	學分	成績	GPA 4.3	GPA 4.0
0	1072	選修	機器學習	3	80	NaN	NaN
1	1072	選修	進階資料結構	3	99	NaN	NaN
2	1072	選修	金融交易系統	3	96	NaN	NaN
3	1071	必修	專題(二)	1	90	NaN	NaN
4	1071	必修	專業倫理-科技倫理	2	90	NaN	NaN

換算成積至4.3/4.0

def four_point_three(grade):
    if grade>=90:
        return 4.3
    elif grade<=89 and grade>=85:
        return 4
    elif grade<=84 and grade>=80:
        return 3.7
    elif grade<=79 and grade>=77:
        return 3.3
    elif grade<=76 and grade>=73:
        return 3.0
    elif grade<=72 and grade>=70:
        return 2.7
    elif grade<=69 and grade>=67:
        return 2.3
    elif grade<=66 and grade>=63:
        return 2.0
    elif grade<=62 and grade>=60:
        return 1.7
    else:
        return 0.0
    
def four(grade):
    if grade>=80:
        return 4.0
    elif grade<=79 and grade>=70:
        return 3.0
    elif grade<=69 and grade>=60:
        return 2.0
    else:
        return 0.0

gpa_four_point_three = []
for i in df['成績'][0:len(df)]:
    gpa_four_point_three.append(four_point_three(i))
    
gpa_four = []
for i in df['成績'][0:len(df)]:
    gpa_four.append(four(i))

df['GPA 4.3'] = gpa_four_point_three
df['GPA 4.0'] = gpa_four
df.head(5) 

	學年度學期	選別	科目名稱	學分	成績	GPA 4.3	GPA 4.0
0	1072	選修	機器學習	3	80	3.7	4.0
1	1072	選修	進階資料結構	3	99	4.3	4.0
2	1072	選修	金融交易系統	3	96	4.3	4.0
3	1071	必修	專題(二)	1	90	4.3	4.0
4	1071	必修	專業倫理-科技倫理	2	90	4.3	4.0

#算總學分
def sum_credit(df):
    credit = 0
    for i in df['學分']:
        credit += i
    return credit

#算成績的
def calculate_grade(df,grade_mode):
    grade = 0
    for i in range(len(df)):
        grade += ( df['學分'][i] * df[grade_mode][i])
    grade /= sum_credit(df)
    return grade

#印出 100 , 4.3 , 4.0 版本
def print_grade(df,grade):
    print("%s" %(grade))
    print("成績總平均 = %.2f" %(calculate_grade(df,'成績')))
    print("GPA 4.3 = %.2f"  %(calculate_grade(df,'GPA 4.3')))
    print("GPA 4.0 = %.2f"  %(calculate_grade(df,'GPA 4.0')))

MAJOR

fliter = (df['選別'] == "必修\u3000")
major = df[fliter] #major's df
major.reset_index(drop=True,inplace=True)
major.head(5)

	學年度學期	選別	科目名稱	學分	成績	GPA 4.3	GPA 4.0
0	1071	必修	專題(二)	1	90	4.3	4.0
1	1071	必修	專業倫理-科技倫理	2	90	4.3	4.0
2	1062	必修	專題(一)	1	90	4.3	4.0
3	1062	必修	數值方法	3	94	4.3	4.0
4	1062	必修	編譯器設計	3	86	4.0	4.0

Last 60

def last60(df):
    limit = 0 # 計算是否會超過 60 的上限
    count = 0 # 計算總共幾個科目

    for i in range(len(df)):
        limit+= df['學分'][i]
        count+=1
        if limit >= 60:
            break
    return df[0:count]

Last60 = last60(df) #last60's df

#df=overall , major , Last60
print_grade(df,'Overall')
print_grade(major,'Major')
print_grade(Last60,'Last 60')

Overall
成績總平均 = 85.43
GPA 4.3 = 3.84
GPA 4.0 = 3.71
Major
成績總平均 = 83.36
GPA 4.3 = 3.65
GPA 4.0 = 3.57
Last 60
成績總平均 = 88.64
GPA 4.3 = 3.97
GPA 4.0 = 3.85