从读取文件行在集合中查找元素

id_set = {'1','2'}
date_set = {'2017-12-19', '2017-12-20'}

# open files for reading and writing
with open('file.txt') as in_file, open('output.txt', 'w') as out_file:

    # write headers
    out_file.write(next(in_file))

    # go over lines in file
    for line in in_file:

        # extract id and date
        id, _, date = line.rstrip().split('|')

        # keep lines have an id or date in the sets
        if id in id_set or date in date_set:
            out_file.write(line)

ID|Name|Date
1|A|2017-12-19
2|B|2017-12-20

import pandas as pd
from io import StringIO

mystr = StringIO("""ID|Name|Date
1|A|2017-12-19
2|B|2017-12-20
3|C|2017-12-21""")

# replace mystr with 'file1.txt'
df = pd.read_csv(mystr, sep='|')

# criteria
id_set = {'1', '2'}
date_set = {'2017-12-19', '2017-12-20'}

# apply criteria
df2 = df[df['ID'].astype(str).isin(id_set) | df['Date'].isin(date_set)]

print(df2)

#   ID Name        Date
# 0  1    A  2017-12-19
# 1  2    B  2017-12-20

# export to csv
df2.to_csv('file1_out.txt', sep='|')