aorzh · February 25, 2020 16:59 · Feb 25, 2020
diff --git a/README.txt b/README.txt
@@ -0,0 +1,18 @@
+task description:
+
+please, write a function that receives
+1)path to file
+2) string to replace
+3) the new string to replace with
+4) in which line in the file to replace (if empty, then replace all)
+
+I assume new string should not be same with pattern
+Line number it's a real number (starts from 1). For example client see in text editor this number and pass it to func. I
+will switch it to index (as it's starts from 0)
+
+I wrapped it's to try/except with custom exception because in this way exceptions more clear and I can manage it.
+I added helper function for write lines because do not necessary write same code twice.
+
+There also possible to use fileinput standard library (https://docs.python.org/3/library/fileinput.html).
+But as multiple files wasn't in requirements I used open() as docs said "If you just want to read or write one file
+see open()."
diff --git a/test.py b/test.py
@@ -0,0 +1,55 @@
+import unittest
+from util import bulk_replace, UtilException
+
+
+class UtilTestCases(unittest.TestCase):
+    def setUp(self):
+        self.filepath = 'test_text'
+        self.pattern = 'foo'
+        self.replace_with = 'bar'
+
+    def test_same_patterns(self):
+        try:
+            bulk_replace(filepath=self.filepath, pattern=self.pattern, replace_with='foo')
+        except UtilException as e:
+            self.assertEqual(e.__str__(), 'pattern and replace_with can not be same')
+
+    def test_line(self):
+        try:
+            bulk_replace(filepath=self.filepath, pattern=self.pattern, replace_with=self.replace_with, line=999)
+        except UtilException as e:
+            self.assertEqual(e.__str__(), 'line not found')
+
+        try:
+            bulk_replace(filepath=self.filepath, pattern=self.pattern, replace_with=self.replace_with, line=-1)
+        except UtilException as e:
+            self.assertEqual(e.__str__(), 'line index should be gte 1')
+
+    def test_replace_one_line(self):
+        bulk_replace(filepath=self.filepath, pattern=self.pattern, replace_with=self.replace_with, line=1)
+        file = open(self.filepath, 'r')
+        line = file.readlines()
+        file.close()
+
+        self.assertEqual(line[0].strip('\n'), self.replace_with)
+        # switch it back
+        bulk_replace(filepath=self.filepath, pattern=self.replace_with, replace_with=self.pattern, line=1)
+
+    def test_replace_all(self):
+        file = open(self.filepath, 'r')
+        old = file.readlines()
+        file.close()
+        bulk_replace(filepath=self.filepath, pattern=self.pattern, replace_with=self.replace_with)
+
+        file = open(self.filepath, 'r')
+        lines = file.readlines()
+        self.assertTrue(self.pattern not in lines)
+
+        # switch it back
+        file = open(self.filepath, 'w')
+        file.writelines(old)
+        file.close()
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/test_text b/test_text
@@ -0,0 +1,5 @@
+foo
+bar
+foo-bar
+bar-foo-bar
+foo-bar-bar
diff --git a/util.py b/util.py
@@ -0,0 +1,48 @@
+class UtilException(Exception):
+    pass
+
+
+def bulk_replace(filepath, pattern, replace_with, line=None):
+    """
+    Function which open file, find necessary pattern and replace it with new fragment.
+    :param filepath: Path to file
+    :param pattern: String to replace
+    :param replace_with: The new string to replace with
+    :param line: In which line in the file to replace (if empty, then replace all)
+    :return:
+    """
+    try:
+        assert pattern != replace_with
+    except AssertionError:
+        raise UtilException('pattern and replace_with can not be same')
+
+    with open(filepath, 'r') as f:
+        text = f.readlines()
+        f.close()
+        if line:  # assume we get line number, not index
+            try:
+                assert line >= 1
+                try:
+                    # replace necessary text
+                    text[line-1] = text[line-1].replace(pattern, replace_with)
+                    _write_lines(filepath, text)
+                except IndexError:
+                    raise UtilException('line not found')
+            except AssertionError:
+                raise UtilException('line index should be gte 1')
+        else:
+            # walk through all lines and replace necessary text
+            lines = [line.replace(pattern, replace_with) for line in text]
+            _write_lines(filepath, lines)
+
+
+def _write_lines(filepath, lines):
+    """
+    Helper function
+    :param filepath: File path to open
+    :param lines: list of lines
+    :return:
+    """
+    with open(filepath, 'w') as f:
+        f.writelines(lines)
+        f.close()
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