>>> EPSG4326 = pyproj.Proj("+init=EPSG:4326")
>>> EPSG3575 = pyproj.Proj("+init=EPSG:3575")
Alternatively you can use the Proj.4 definition, so the following two lines are doing the same, you can use either of them
EPSG3995 = pyproj.Proj("+proj=stere +lat_0=90 +lat_ts=71 +lon_0=0 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs ")
EPSG3995 = pyproj.Proj("+init=EPSG:3995")
Now you can define the input coordinates and transform them, in this example you transform values from EPSG:4326 to EPSG:3575:
>>> lat = 79
>>> long = -5
>>> x, y = pyproj.transform(EPSG4326, EPSG3575, long, lat)
>>> x,y
(8768866.779113682, -3366052.584518589)
Official documentation can be found here