part_50 = df.sample(frac = 0.5) code example

Example 1: pandas sample seed

>>> df.sample(frac=0.5, replace=True, random_state=1)
      num_legs  num_wings  num_specimen_seen
dog          4          0                  2
fish         0          0                  8

Example 2: sample based on column pandas

df1 = df[df['a']==1].sample(n=50)
df0 = df[df['a']==0].sample(n=50)
print(pd.concat([df1,df0]))