在Python中前后搜索循环

Question

我有一个Python字典，每100个单位我有一个特定的值

from collections import defaultdict
nan = np.nan

points_dict_avg[100].append(10)
points_dict_avg[200].append(10)
points_dict_avg[300].append(10)
points_dict_avg[400].append(nan)

对于确定键我需要提取存储在字典中的信息

mykey = 400

如果值为nan，我希望选择上方或下方的值，并向后减去0.08到向后的值，或在向前减去0.08

#backward example

avg_dem_value = points_dict_avg[mykey][0]
while math.isnan(avg_dem_value):
    new_mykey = mykey - 100
    avg_dem = points_dict_avg[new_mykey][0]
    avg_dem_value = avg_dem - 0.8

#forward example
points_dict_avg = defaultdict(list)
points_dict_avg[100].append(nan)
points_dict_avg[200].append(10)
points_dict_avg[300].append(10)
points_dict_avg[400].append(10)
mykey = 100

avg_dem_value = points_dict_avg[mykey][0]
while math.isnan(avg_dem_value):
    new_mykey = mykey + 100
    avg_dem = points_dict_avg[new_mykey][0]
    avg_dem_value = avg_dem + 0.8

我希望在同一个循环中找到一个方法，同时向前和向前看，直到建立一个值，我命令避免IndexError: list index out of range

*#UPDATE: I find now this solution not very elegant with two while cycle. the first for backward and the second for forward. This is an example*

points_dict_avg = defaultdict(list)
points_dict_avg[100].append(nan)
points_dict_avg[200].append(nan)
points_dict_avg[300].append(nan)
points_dict_avg[400].append(40)
dem_value = 100

avg_dem_value = points_dict_avg[dem_value][0]
dem_value_back = dem_value
while math.isnan(avg_dem_value):
    dem_value_back = dem_value_back - 100
    try:
        avg_dem = points_dict_avg[dem_value_back][0]
    except:
        avg_dem_value = nan
        break
    avg_dem_value = avg_dem - 0.08
dem_value_forw = dem_value
while math.isnan(avg_dem_value):
    dem_value_forw = dem_value_forw + 100
    try:
       avg_dem = points_dict_avg[dem_value_forw][0]
    except:
        avg_dem_value = nan
        break
    avg_dem_value = avg_dem + 0.08