Per my comment on issue16569, the overhead of performing one seek before each (raw file data) read is quite minimal. I have attached a new (but incomplete) patch, on which the following microbenchmarks are based. The patch is essentially identical to Stepan's 2012 patch, except I haven't yet decided how best to preserve the semantics of ZipFile.close().

"my.zip" is the same my.zip from issue22842. It contains 10,000 files each containing 10 bytes over 2 lines.

"my2.zip" contains 8,000 files each containing the same copy of 64kb of /dev/urandom output. The resulting ZIP is 500mb.

For each test, the first run is the existing zipfile module, and the second run is with the patch. In summary:

* There is a 35% perf increase in str mode when handling many small files (on OS X at least)
* There is a 6% perf decrease in file mode when handling small sequential reads.
* There is a 2.4% perf decrease in file mode when handling large sequential reads.


From my reading of zipfile.py, it is clear there are _many_ ways to improve its performance (probably starting with readline()), and rejection of a functional fix should almost certainly be at the bottom of that list.


For each of the tests below, the functions used were:

    def a():
        """
        Test concurrent line reads to a str mode ZipFile.
        """
        zf = zipfile.ZipFile('my2.zip')
        members = [zf.open(n) for n in zf.namelist()]
        for m in members:
            m.readline()
        for m in members:
            m.readline()

    def c():
        """
        Test sequential small reads to a str mode ZipFile.
        """
        zf = zipfile.ZipFile('my2.zip')
        for name in zf.namelist():
            with zf.open(name) as zfp:
                zfp.read(1000)

    def d():
        """
        Test sequential small reads to a file mode ZipFile.
        """
        fp = open('my2.zip', 'rb')
        zf = zipfile.ZipFile(fp)
        for name in zf.namelist():
            with zf.open(name) as zfp:
                zfp.read(1000)

    def e():
        """
        Test sequential large reads to a file mode ZipFile.
        """
        fp = open('my2.zip', 'rb')
        zf = zipfile.ZipFile(fp)
        for name in zf.namelist():
            with zf.open(name) as zfp:
                zfp.read()


---- my.zip ----

$ python3.4 -m timeit -s 'import my' 'my.a()'
10 loops, best of 3: 1.47 sec per loop

$ python3.4 -m timeit -s 'import my' 'my.a()'
10 loops, best of 3: 950 msec per loop

---

$ python3.4 -m timeit -s 'import my' 'my.c()'
10 loops, best of 3: 1.3 sec per loop

$ python3.4 -m timeit -s 'import my' 'my.c()'
10 loops, best of 3: 865 msec per loop

---

$ python3.4 -m timeit -s 'import my' 'my.d()'
10 loops, best of 3: 800 msec per loop

$ python3.4 -m timeit -s 'import my' 'my.d()'
10 loops, best of 3: 851 msec per loop


---- my2.zip ----

$ python3.4 -m timeit -s 'import my' 'my.a()'
10 loops, best of 3: 1.46 sec per loop

$ python3.4 -m timeit -s 'import my' 'my.a()'
10 loops, best of 3: 1.16 sec per loop

---

$ python3.4 -m timeit -s 'import my' 'my.c()'
10 loops, best of 3: 1.13 sec per loop

$ python3.4 -m timeit -s 'import my' 'my.c()'
10 loops, best of 3: 892 msec per loop

---

$ python3.4 -m timeit -s 'import my' 'my.d()'
10 loops, best of 3: 842 msec per loop

$ python3.4 -m timeit -s 'import my' 'my.d()'
10 loops, best of 3: 882 msec per loop

---

$ python3.4 -m timeit -s 'import my' 'my.e()'
10 loops, best of 3: 1.65 sec per loop

$ python3.4 -m timeit -s 'import my' 'my.e()'
10 loops, best of 3: 1.69 sec per loop