Python

Loops

Files in a directory

import os

directory = os.fsencode(directory_in_str)

for file in os.listdir(directory):
    filename = os.fsdecode(file)
    if filename.endswith(".txt"): 
        print("Found a text file"))
        continue
    else:
        continue

Lines in a file

file = open("input.txt", "r")
for line in file:
    print(line)

Pandas

Conditionally create a column based on another column.

source

def function(row):
    if row["A"] == row["B"]:
        val = 0
    elif row["A"] > row["B"]:
        val = 1
    else:
        val = -1
    return val


df["C"] = df.apply(f, axis=1)

Fill null values

df = df.fillna("")

Rename columns

df = df.rename(columns={"old_name": "new_name"})

Remove columns

df = df.remove(columns=["column_a", "column_b"])

Types

Check if string is a valid integer

"14".isdigit()

Lists

Test is one list is in another list

any(map(lambda v: v in list2, list1))