sed

Sample

To replace item with object in every file in the current folder:

find . -type f | xargs sed -i s/abc_item/xyz_item/g

To replace hatherleigh with village in all .py files in the current folder and sub-folders:

find . -name "*.py" | xargs sed -i 's/hatherleigh/village/g'
find . -name "models.py" | xargs sed -i 's/__unicode__/__str__/g'