Import

Some Python programs use no import statements. But more often, programs require access to external packages and their modules.

Directives

With the from and import directives, we include those names into a program. This avoids errors. The star syntax may also be used.

Example

This program requires the date and timedelta modules from the datetime package. It signals this by using an asterisk (star) after the import keyword.

Tip The star character means "import all." All submodules of datetime are imported.

Warning This program is correct. But if you remove the "from import" statement, it will result in NameErrors.

from datetime import *

def yesterday():
    today = date.today()
    yesterday = today - timedelta(days=1)
    return yesterday

print(date.today())
print(yesterday())2014-04-17
2014-04-16

Alternate syntax

The star syntax is not the only option. We can specify the modules directly, by naming them. This may be preferred in many projects.

Tip We can specify multiple modules from one package using a comma between each name. This reduces the line count of the program.

from datetime import date, timedeltafrom datetime import date
from datetime import timedelta

`NameError`

A NameError is often caused by a missing import statement. Consider this program. It correctly imports date, but lacks the timedelta import that it needs.

However The program fails at the line where we assign "yesterday." The print statement is never reached.

from datetime import date

today = date.today()
yesterday = today - timedelta(days=1)
print(yesterday)Traceback (most recent call last):
  File "C:\programs\file.py", line 8, in <module>
    yesterday = today - timedelta(days=1)
NameError: name 'timedelta' is not defined

Custom

Here we use a custom Python module. Please create a new Python file in the same directory as your Python program. Give it a name.

Then In the Python program, use the import statement to include it. You can call methods in the module.

Tip The module file must be in the same directory as your program. And its name must equal the name in your "import" statement.

def buy():
    print("stock.buy called")import stock

# Call the method in the stock module.
stock.buy()
stock.buy called

Python programs can become complex. With the import statement, and its associated keyword "from," we bring in external package resources to our program.