bmp180 is a micropython module for the Bosch BMP180 sensor. It measures temperature as well as pressure, with a high enough resolution to calculate altitude.
Breakoutboard: http://www.adafruit.com/products/1603
data-sheet: http://ae-bst.resource.bosch.com/media/products/dokumente/bmp180/BST-BMP180-DS000-09.pdf

Example:

from bmp180 import BMP180
bmp180 = BMP180()
bmp180.oversample_sett = 2
temp = bmp180.get_temperature()
baseline = bmp180.baseline(1000)
p = bmp180.get_pressure()
altitude = bmp180.get_altitude()
print(temp, baseline, p, altitude)

Note that in this example the altitude will be around zero, because the pressure measurment is done immediatly after the baseline setting.

BMP180
Module for the BMP180 pressure sensor.

get_altitude()
Calculates and returns the altitude relative to a the baseline.

baseline(dt=None)
Measures the pressure for a given time and sets the baseline to
the mean of the measurements. If no dt is given it will default
to 10 seconds.

gauge_pressure()
Starts the pressure measurement and sets the time it will be
finished.

gauge_temperature()
Starts the temperature measurement and sets the time it will be
finished.

get_pressure()
Returns the pressure. If not gauged first, it will do that first.

get_temperature()
Returns the temperature. If not gauged first, it will do that first.

chip_id
ID of chip is hardcoded on the sensor.

oversample_sett
Sets the accuracy. Default: 0

• 0 lowest accuracy, fastest
• 1
• 2
• 3 highest accuracy, slowest

baseline
Pressure at Main Sea Level. The default is 101325 Pa, but you can use your local QNH in Pa.
When evoked, the method baseline(dt) sets this variable to the local pressure. To get different altitudes, use this as baselines:

temp_comp_sample_rate
The refresh rate of the temperature measurment for compensating pressure in Hz.