python问题错哪了

boys=['aas','das','eqqe']
girls=['das','dsae','we']
girlletter={}
for girl in girls:
girlletter.setdefault(girl[0],[]).append(girl)
print[b+'+'+g for b in boys for g in girlletter[b[0]]]

Traceback (most recent call last):
File "D:/Python27/新建文件夹/22.py", line 6, in
print[b+'+'+g for b in boys for g in girlletter[b[0]]]
KeyError: 'a'

boys=['aas','das','eqqe']
girls=['das','dsae','we']
girlletter={}
for girl in girls:
    girlletter.setdefault(girl[0],[]).append(girl)

print girlletter  #输出为{'d': ['das', 'dsae'], 'w': ['we']}
print[b+'+'+g for b in boys for g in girlletter[b[0]]]  # b[0]为a,而girlletter中无此key

string=[] sum1=0 count1=0 sum2=0 count2=0 sum3=0 count3=0 fp=open(r'score.txt','r') for i in fp.readlines():     i.strip()     string.append(i.split()) for j in string:     if j[1]=="女":         sum1=sum1+int(j[3])         count1=count1+1     else:         sum2=sum2+int(j[3])         count2=count2+1     if j[2]=="python程序设计":         sum3=sum3+int(j[3])         count3=count3+1 print("该班女生成绩是：",sum1 / count1) print("该班男生成绩是：",sum2 / count2) print("该班《python程序设计》成绩是：",sum3 / count3)