You can use the pandas.DataFrame.quantile() function, as shown below.
import pandas as pd
import random
A = [ random.randint(0,100) for i in range(10) ]
B = [ random.randint(0,100) for i in range(10) ]
df = pd.DataFrame({ 'field_A': A, 'field_B': B })
df
# field_A field_B
# 0 90 72
# 1 63 84
# 2 11 74
# 3 61 66
# 4 78 80
# 5 67 75
# 6 89 47
# 7 12 22
# 8 43 5
# 9 30 64
df.field_A.mean() # Same as df['field_A'].mean()
# 54.399999999999999
df.field_A.median()
# 62.0
# You can call `quantile(i)` to get the i'th quantile,
# where `i` should be a fractional number.
df.field_A.quantile(0.1) # 10th percentile
# 11.9
df.field_A.quantile(0.5) # same as median
# 62.0
df.field_A.quantile(0.9) # 90th percentile
# 89.10000000000001